Life is great and everything will be OK, Kotlin is here (Google IO 2017)

Using Kotlin for Android development has grown in popularity over the past few years and is now officially supported by Google. If you are not already using Kotlin you might be wondering why and how to adopt it. In the first part of this talk, Jake will cover advancing the usage and design patterns of the language for Android development to solve larger problems. In the second part, Christina will share her experience using Kotlin in production, from mistakes to successes, and help you answer questions your team/company might ask about adopting it.

Video: https://youtu.be/fPzxfeDJDzY

Transcript

1. +Christina Lee
   @RunChristinaRun
   +Jake Wharton
   @JakeWharton
   Kotlin is here
   Life is great and everything will be OK
   

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2. MainActivity.java
   public class MainActivity extends Activity {
   @Override
   protected void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   }1
   }2
   

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3. MainActivity.java
   public class MainActivity extends Activity {
   @Override
   protected void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   }1
   }2
   

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4. MainActivity.java
   public class MainActivity extends Activity {
   @Override
   protected void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   }1
   }2
   

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5. MainActivity.java
   public class MainActivity extends Activity {
   @Override
   protected void onCreate(@Nullable Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   }1
   }2
   @Nullable
   

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6. MainActivity.java
   public class MainActivity extends Activity {
   @Override
   protected void onCreate(@Nullable Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   }1
   }2
   

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7. MainActivity.kt
   class MainActivity : Activity() {
   override fun onCreate(savedInstanceState: Bundle?) {
   super.onCreate(savedInstanceState)
   }1
   }2
   

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8. MainActivity.kt
   class MainActivity : Activity() {
   override fun onCreate(savedInstanceState: Bundle?) {
   super.onCreate(savedInstanceState)
   }1
   }2
   

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9. MainActivity.kt
   class MainActivity : Activity() {
   override fun onCreate(savedInstanceState: Bundle?) {
   super.onCreate(savedInstanceState)
   }1
   }2
   

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10. TextView.java
    public float getAlpha() {
    // Retrieve value...
    }
    

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11. TextView.java
    public float getAlpha() {
    // Retrieve value...
    }
    public void setAlpha(float alpha) {
    // Set value...
    }
    

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12. TextView.java
    public float getAlpha() {
    // Retrieve value...
    }
    public void setAlpha(float alpha) {
    // Set value...
    }
    TextView tv = // ...
    Log.d("MainActivity", "Alpha: " + tv.getAlpha());
    tv.setAlpha(0f);
    MainActivity.java
    

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13. TextView.java
    public float getAlpha() {
    // Retrieve value...
    }
    public void setAlpha(float alpha) {
    // Set value...
    }
    MainActivity.kt
    val tv = // ...
    Log.d("MainActivity", "Alpha: " + tv.alpha)
    tv.alpha = 0f
    

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14. TextView.java
    public float getAlpha() {
    // Retrieve value...
    }1
    public void setAlpha(float alpha) {
    // Set value...
    }2
    MainActivity.kt
    val tv = // ...
    Log.d("MainActivity", "Alpha: " + tv.alpha)
    tv.alpha = 0f
    

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15. TextView.java
    public float getAlpha() {
    // Retrieve value...
    }1
    public void setAlpha(float alpha) {
    // Set value...
    }2
    MainActivity.kt
    val tv = // ...
    Log.d("MainActivity", "Alpha: " + tv.alpha)
    tv.alpha = 0f
    

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16. TextView.java
    public float getAlpha() {
    // Retrieve value...
    }1
    public void setAlpha(float alpha) {
    // Set value...
    }2
    MainActivity.kt
    val tv = // ...
    Log.d("MainActivity", "Alpha: " + tv.alpha)
    tv.alpha = 0f
    

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17. MainActivity.java
    LinearLayout views = // ...
    for (int i = 0; i < views.getChildCount(); i++) {
    View view = views.getChildAt(i);
    // TODO do something with view
    }
    

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18. MainActivity.kt
    val views = // ...
    for (index in 0 until views.childCount) {
    val view = views.getChildAt(index)
    // TODO do something with view
    }
    

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19. MainActivity.kt
    val views = // ...
    for (index in 0 until views.childCount) {
    val view = views.getChildAt(index)
    // TODO do something with view
    }1
    

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20. MainActivity.kt
    val views = // ...
    for (index in 0 until views.childCount) {
    val view = views.getChildAt(index)
    // TODO do something with view
    }1
    

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21. MainActivity.kt
    val views = // ...
    for (index in 0 until views.childCount) {
    val view = views.getChildAt(index)
    // TODO do something with view
    }
    

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22. MainActivity.kt
    val views = // ...
    for (index in 0 until views.childCount) {Z
    val view = views.getChildAt(index)
    // TODO do something with view
    }1
    ViewGroups.kt
    fun ViewGroup.forEach(action: (View) -> Unit) {
    for (index in 0 until childCount) {
    action(getChildAt(index))
    }2
    }3
    . Each ->
    

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23. MainActivity.kt
    val views = // ...
    views.forEach {Zview ->
    // TODO do something with view
    }1
    ViewGroups.kt
    fun ViewGroup.forEach(action: (View) -> Unit) {
    for (index in 0 until childCount) {
    action(getChildAt(index))
    }2
    }3
    val = views.getChildAt(i)
    

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24. MainActivity.kt
    val views = // ...
    views.forEach {Zview ->
    // TODO do something with view
    }1
    ViewGroups.kt
    fun ViewGroup.forEach(action: (View) -> Unit) {
    for (index in 0 until childCount) {
    action(getChildAt(index))
    }2
    }3
    

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25. MainActivity.kt
    val views = // ...
    views.forEach {Zview ->
    // TODO do something with view
    }1
    ViewGroups.kt
    fun ViewGroup.forEach(action: (View) -> Unit) {
    for (index in 0 until childCount) {
    action(getChildAt(index))
    }2
    }3
    

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26. MainActivity.kt
    val views = // ...
    views.forEach {Zview ->
    // TODO do something with view
    }1
    ViewGroups.kt
    fun ViewGroup.forEach(action: (View) -> Unit) {
    for (index in 0 until childCount) {
    action(getChildAt(index))
    }2
    }3
    

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27. MainActivity.kt
    val views = // ...
    views.forEach {Zview ->
    // TODO do something with view
    }1
    ViewGroups.kt
    fun ViewGroup.forEach(action: (View) -> Unit) {
    for (index in 0 until childCount) {
    action(getChildAt(index))
    }2
    }3
    

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28. MainActivity.kt
    val views = // ...
    views.forEach {Zview ->
    // TODO do something with view
    }1
    ViewGroups.kt
    inline fun ViewGroup.forEach(action: (View) -> Unit) {
    for (index in 0 until childCount) {
    action(getChildAt(index))
    }2
    }3
    inline
    

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29. MainActivity.kt
    val views = // ...
    views.forEach {Zview ->
    // TODO do something with view
    }1
    ViewGroups.kt
    inline fun ViewGroup.forEach(action: (View) -> Unit) {
    for (index in 0 until childCount) {
    action(getChildAt(index))
    }2
    }3
    

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30. MainActivity.kt
    val views = // ...
    views.forEach {Zview -> /* ... */ }1
    views.forEachIndexed { index, view -> /* ... */ }1
    ViewGroups.kt
    inline fun ViewGroup.forEach(action: (View) -> Unit) {
    for (index in 0 until childCount) {
    action(getChildAt(index))
    }2
    }3
    inline fun ViewGroup.forEachIndexed(action: (Int, View) -> Unit) {
    for (index in 0 until childCount) {
    action(index, getChildAt(index))
    }
    }
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31. MainActivity.kt
    val views = // ...
    views.forEach {Zview -> /* ... */ }1
    views.forEachIndexed { index, view -> /* ... */ }1
    ViewGroups.kt
    inline fun ViewGroup.forEach(action: (View) -> Unit) {
    for (index in 0 until childCount) {
    action(getChildAt(index))
    }2
    }3
    inline fun ViewGroup.forEachIndexed(action: (Int, View) -> Unit) {
    for (index in 0 until childCount) {
    action(index, getChildAt(index))
    }
    }
    /
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32. MainActivity.kt
    val views = // ...
    /
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    ViewGroups.kt
    operator fun ViewGroup.get(index: Int): View? = getChildAt(index)
    

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33. MainActivity.kt
    val views = // ...
    val first = views[0]
    ViewGroups.kt
    operator fun ViewGroup.get(index: Int): View? = getChildAt(index)
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34. MainActivity.kt
    val views = // ...
    val first = views[0]
    ViewGroups.kt
    operator fun ViewGroup.get(index: Int): View? = getChildAt(index)
    /
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35. MainActivity.kt
    val views = // ...
    val first = views[0]
    ViewGroups.kt
    operator fun ViewGroup.get(index: Int): View? = getChildAt(index)
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36. MainActivity.kt
    val views = // ...
    val first = views[0]
    views -= first
    ViewGroups.kt
    operator fun ViewGroup.get(index: Int): View? = getChildAt(index)
    operator fun ViewGroup.minusAssign(child: View) = removeView(child)
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37. MainActivity.kt
    val views = // ...
    val first = views[0]
    views -= first
    ViewGroups.kt
    operator fun ViewGroup.get(index: Int): View? = getChildAt(index)
    operator fun ViewGroup.minusAssign(child: View) = removeView(child)
    /
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38. MainActivity.kt
    val views = // ...
    val first = views[0]
    views -= first
    views += first
    ViewGroups.kt
    operator fun ViewGroup.get(index: Int): View? = getChildAt(index)
    operator fun ViewGroup.minusAssign(child: View) = removeView(child)
    operator fun ViewGroup.plusAssign(child: View) = addView(child)
    /
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39. MainActivity.kt
    val views = // ...
    val first = views[0]
    views -= first
    views += first
    ViewGroups.kt
    operator fun ViewGroup.get(index: Int): View? = getChildAt(index)
    operator fun ViewGroup.minusAssign(child: View) = removeView(child)
    operator fun ViewGroup.plusAssign(child: View) = addView(child)
    /
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40. MainActivity.kt
    val views = // ...
    val first = views[0]
    views -= first
    views += first
    if (first in views) doSomething()
    ViewGroups.kt
    operator fun ViewGroup.get(index: Int): View? = getChildAt(index)
    operator fun ViewGroup.minusAssign(child: View) = removeView(child)
    operator fun ViewGroup.plusAssign(child: View) = addView(child)
    operator fun ViewGroup.contains(child: View) = indexOfChild(child) != -1
    /
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41. MainActivity.kt
    val views = // ...
    val first = views[0]
    views -= first
    views += first
    if (first in views) doSomething()
    ViewGroups.kt
    operator fun ViewGroup.get(index: Int): View? = getChildAt(index)
    operator fun ViewGroup.minusAssign(child: View) = removeView(child)
    operator fun ViewGroup.plusAssign(child: View) = addView(child)
    operator fun ViewGroup.contains(child: View) = indexOfChild(child) != -1
    /
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42. MainActivity.kt
    val views = // ...
    val first = views[0]
    views -= first
    views += first
    if (first in views) doSomething()
    ViewGroups.kt
    operator fun ViewGroup.get(index: Int): View? = getChildAt(index)
    operator fun ViewGroup.minusAssign(child: View) = removeView(child)
    operator fun ViewGroup.plusAssign(child: View) = addView(child)
    operator fun ViewGroup.contains(child: View) = indexOfChild(child) != -1
    /
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43. MainActivity.kt
    val views = // ...
    val first = views[0]
    views -= first
    views += first
    if (first in views) doSomething()
    ViewGroups.kt
    operator fun ViewGroup.get(index: Int): View? = getChildAt(index)
    operator fun ViewGroup.minusAssign(child: View) = removeView(child)
    operator fun ViewGroup.plusAssign(child: View) = addView(child)
    operator fun ViewGroup.contains(child: View) = indexOfChild(child) != -1
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44. MainActivity.kt
    val views = // ...
    val first = views[0]
    views -= first
    views += first
    if (first in views) doSomething()
    ViewGroups.kt
    operator fun ViewGroup.get(index: Int): View? = getChildAt(index)
    operator fun ViewGroup.minusAssign(child: View) = removeView(child)
    operator fun ViewGroup.plusAssign(child: View) = addView(child)
    operator fun ViewGroup.contains(child: View) = indexOfChild(child) != -1
    /
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45. MainActivity.kt
    val views = // ...
    val first = views.get(0)
    views.minusAssign(first)
    views.plusAssign(first)
    if (views.contains(first)) doSomething()
    ViewGroups.kt
    operator fun ViewGroup.get(index: Int): View? = getChildAt(index)
    operator fun ViewGroup.minusAssign(child: View) = removeView(child)
    operator fun ViewGroup.plusAssign(child: View) = addView(child)
    operator fun ViewGroup.contains(child: View) = indexOfChild(child) != -1
    /
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    in
    

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46. MainActivity.kt
    val views = // ...
    val first = views[0]
    views -= first
    views += first
    if (first in views) doSomething()
    ViewGroups.kt
    operator fun ViewGroup.get(index: Int): View? = getChildAt(index)
    operator fun ViewGroup.minusAssign(child: View) = removeView(child)
    operator fun ViewGroup.plusAssign(child: View) = addView(child)
    operator fun ViewGroup.contains(child: View) = indexOfChild(child) != -1
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47. MainActivity.kt
    val views = // ...
    val first = views[0]
    views -= first
    views += first
    if (first in views) doSomething()
    Log.d("MainActivity", "View count: ${views.size}")
    ViewGroups.kt
    operator fun ViewGroup.get(index: Int): View? = getChildAt(index)
    operator fun ViewGroup.minusAssign(child: View) = removeView(child)
    operator fun ViewGroup.plusAssign(child: View) = addView(child)
    operator fun ViewGroup.contains(child: View) = indexOfChild(child) != -1
    val ViewGroup.size: Int
    get() = childCount
    /
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48. MainActivity.kt
    val views = // ...
    val first = views[0]
    views -= first
    views += first
    if (first in views) doSomething()
    Log.d("MainActivity", "View count: ${views.size}")
    ViewGroups.kt
    operator fun ViewGroup.get(index: Int): View? = getChildAt(index)
    operator fun ViewGroup.minusAssign(child: View) = removeView(child)
    operator fun ViewGroup.plusAssign(child: View) = addView(child)
    operator fun ViewGroup.contains(child: View) = indexOfChild(child) != -1
    val ViewGroup.size: Int
    get() = childCount
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49. MainActivity.kt
    val views = // ...
    val first = views[0]
    views -= first
    views += first
    if (first in views) doSomething()
    Log.d("MainActivity", "View count: ${views.size}")
    ViewGroups.kt
    operator fun ViewGroup.get(index: Int): View? = getChildAt(index)
    operator fun ViewGroup.minusAssign(child: View) = removeView(child)
    operator fun ViewGroup.plusAssign(child: View) = addView(child)
    operator fun ViewGroup.contains(child: View) = indexOfChild(child) != -1
    val ViewGroup.size: Int
    get() = childCount
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50. MainActivity.kt
    val views = // ...
    val first = views[0]
    views -= first
    views += first
    if (first in views) doSomething()
    Log.d("MainActivity", "View count: ${views.size}")
    ViewGroups.kt
    operator fun ViewGroup.get(index: Int): View? = getChildAt(index)
    operator fun ViewGroup.minusAssign(child: View) = removeView(child)
    operator fun ViewGroup.plusAssign(child: View) = addView(child)
    operator fun ViewGroup.contains(child: View) = indexOfChild(child) != -1
    val ViewGroup.size: Int
    get() = childCount
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51. MainActivity.kt
    val views = // ...
    val first = views[0]
    views -= first
    views += first
    if (first in views) doSomething()
    Log.d("MainActivity", "View count: ${views.size}")
    ViewGroups.kt
    operator fun ViewGroup.get(index: Int): View? = getChildAt(index)
    operator fun ViewGroup.minusAssign(child: View) = removeView(child)
    operator fun ViewGroup.plusAssign(child: View) = addView(child)
    operator fun ViewGroup.contains(child: View) = indexOfChild(child) != -1
    val ViewGroup.size: Int
    get() = childCount
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52. MainActivity.kt
    val views = // ...
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    ViewGroups.kt
    fun ViewGroup.children() = object : Iterable {
    override fun iterator() = object : Iterator {
    var index = 0
    override fun hasNext() = index < childCount
    override fun next() = getChildAt(index++)
    }
    }
    

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53. MainActivity.kt
    val views = // ...
    for (view in views.children()) {
    // TODO do something with view
    }1
    ViewGroups.kt
    fun ViewGroup.children() = object : Iterable {
    override fun iterator() = object : Iterator {
    var index = 0
    override fun hasNext() = index < childCount
    override fun next() = getChildAt(index++)
    }2
    }3
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54. MainActivity.kt
    val views = // ...
    for (view in views.children()) {
    // TODO do something with view
    }1
    val visibleHeight = views.children()
    .filter { it.visibility == View.VISIBLE }
    .sumBy { it.measuredHeight }
    ViewGroups.kt
    fun ViewGroup.children() = object : Iterable {
    override fun iterator() = object : Iterator {
    var index = 0
    override fun hasNext() = index < childCount
    override fun next() = getChildAt(index++)
    }2
    }3
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55. MainActivity.kt
    val views = // ...
    for (view in views.children()) {
    // TODO do something with view
    }
    val visibleHeight = views.children()
    .filter { it.visibility == View.VISIBLE }
    .sumBy { it.measuredHeight }
    ViewGroups.kt
    fun ViewGroup.children() = object : Iterable {
    override fun iterator() = object : Iterator {
    var index = 0
    override fun hasNext() = index < childCount
    override fun next() = getChildAt(index++)
    }
    }
    /
    / T
    O
    D
    O d
    o s
    o
    m
    e
    t
    h
    i
    n
    g w
    i
    t
    h v
    i
    e
    w
    

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56. MainActivity.java
    Trace.beginSection(sectionName);
    expensiveCalculation();
    Trace.endSection();
    

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57. MainActivity.java
    Trace.beginSection(sectionName);
    expensiveCalculation();
    Trace.endSection();
    Traces.kt
    inline fun trace(sectionName: String, body: () -> Unit) {
    Trace.beginSection(sectionName)
    try {
    body()
    }2finally {
    Trace.endSection()
    }3
    }4
    

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58. Traces.kt
    inline fun trace(sectionName: String, body: () -> Unit) {Z
    Trace.beginSection(sectionName)
    try {
    body()
    }2finally {
    Trace.endSection()
    }3
    }4
    MainActivity.kt
    trace("foo") {
    expensiveCalculation()
    }1
    

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59. Traces.kt
    inline fun trace(sectionName: String, body: () -> T): T {Z
    Trace.beginSection(sectionName)
    try {
    return body()
    }2finally {
    Trace.endSection()
    }3
    }4
    Unit
    MainActivity.kt
    trace("foo") {
    expensiveCalculation()
    }1
    T T
    return
    

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60. Traces.kt
    inline fun trace(sectionName: String, body: () -> T): T {Z
    Trace.beginSection(sectionName)
    try {
    return body()
    }2finally {
    Trace.endSection()
    }3
    }4
    MainActivity.kt
    val result = trace("foo") {
    expensiveCalculation()
    }1
    val result =
    T T
    return
    

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61. Traces.kt
    inline fun trace(sectionName: String, body: () -> T): T {Z
    Trace.beginSection(sectionName)
    try {
    return body()
    }2finally {
    Trace.endSection()
    }3
    }4
    MainActivity.kt
    val result = trace("foo") {
    expensiveCalculation()
    }1
    

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62. MainActivity.java
    SQLiteDatabase db = // ...
    db.beginTransaction();
    try {
    db.delete("users", "first_name = ?", new String[] { "jake" });
    } finally {
    db.endTransaction();
    }1
    

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63. MainActivity.java
    SQLiteDatabase db = // ...
    db.beginTransaction();
    try {
    db.delete("users", "first_name = ?", new String[] { "jake" });
    db.setTransactionSuccessful();
    } finally {
    db.endTransaction();
    }1
    

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64. SQLiteDatabase db = // ...
    db.beginTransaction();
    try {
    db.delete("users", "first_name = ?", new String[] { "jake" });
    db.setTransactionSuccessful();
    } finally {
    db.endTransaction();
    }1
    Databases.kt
    inline fun SQLiteDatabase.transaction(body: () -> Unit) {
    beginTransaction()
    try {
    body()
    setTransactionSuccessful()
    } finally {
    endTransaction()
    }2
    }1
    

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65. MainActivity.kt
    val db = // ...
    db.transaction {4
    db.delete("users", "first_name = ?", arrayOf("jake"))
    }3
    Databases.kt
    inline fun SQLiteDatabase.transaction(body: () -> Unit) {
    beginTransaction()
    try {
    body()X
    setTransactionSuccessful()
    } finally {
    endTransaction()
    }2
    }1 1
    SQLiteDatabase
    db.beginTransaction();
    try
    new String[] { }
    db.setTransactionSuccessful();
    finally {
    db.endTransaction();
    }1
    

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66. MainActivity.kt
    val db = // ...
    db.transaction {4
    db.delete("users", "first_name = ?", arrayOf("jake"))
    }3
    Databases.kt
    inline fun SQLiteDatabase.transaction(body: () -> Unit) {
    beginTransaction()
    try {
    body()X
    setTransactionSuccessful()
    } finally {
    endTransaction()
    }2
    }1 1
    

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67. MainActivity.kt
    val db = // ...
    db.transaction {4
    db.delete("users", "first_name = ?", arrayOf("jake"))
    }3
    Databases.kt
    inline fun SQLiteDatabase.transaction(body: () -> Unit) {
    beginTransaction()
    try {
    body()X
    setTransactionSuccessful()
    } finally {
    endTransaction()
    }2
    }1 1
    

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68. MainActivity.kt
    val db = // ...
    db.transaction {4
    db.delete("users", "first_name = ?", arrayOf("jake"))
    }3
    Databases.kt
    inline fun SQLiteDatabase.transaction(body: (SQLiteDatabase) -> Unit) {
    beginTransaction()
    try {
    body()X
    setTransactionSuccessful()
    } finally {
    endTransaction()
    }2
    }1 1
    SQLiteDatabase
    

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69. MainActivity.kt
    val db = // ...
    db.transaction {4
    db.delete("users", "first_name = ?", arrayOf("jake"))
    }3
    Databases.kt
    inline fun SQLiteDatabase.transaction(body: (SQLiteDatabase) -> Unit) {
    beginTransaction()
    try {
    body(this)X
    setTransactionSuccessful()
    } finally {
    endTransaction()
    }2
    }1 1
    SQLiteDatabase
    body(this)X
    

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70. MainActivity.kt
    val db = // ...
    db.transaction {4
    it.delete("users", "first_name = ?", arrayOf("jake"))
    }3
    Databases.kt
    inline fun SQLiteDatabase.transaction(body: (SQLiteDatabase) -> Unit) {
    beginTransaction()
    try {
    body(this)
    setTransactionSuccessful()
    } finally {
    endTransaction()
    }2
    }1 1
    it.delete
    SQLiteDatabase
    body(this)X
    

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71. MainActivity.kt
    val db = // ...
    db.transaction {4
    it.delete("users", "first_name = ?", arrayOf("jake"))
    }3
    Databases.kt
    inline fun SQLiteDatabase.transaction(body: (SQLiteDatabase) -> Unit) {
    beginTransaction()
    try {
    body(this)F
    setTransactionSuccessful()
    } finally {
    endTransaction()
    }2
    }1 1
    

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72. MainActivity.kt
    val db = // ...
    db.transaction {4
    it.delete("users", "first_name = ?", arrayOf("jake"))
    }3
    Databases.kt
    inline fun SQLiteDatabase.transaction(body: (SQLiteDatabase) -> Unit) {
    beginTransaction()
    try {
    body(this)F
    setTransactionSuccessful()
    } finally {
    endTransaction()
    }2
    }1 1
    

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73. MainActivity.kt
    val db = // ...
    db.transaction {4
    it.delete("users", "first_name = ?", arrayOf("jake"))
    }3
    Databases.kt
    inline fun SQLiteDatabase.transaction(body: (SQLiteDatabase) -> Unit) {
    beginTransaction()
    try {
    body(this)F
    setTransactionSuccessful()
    } finally {
    endTransaction()
    }2
    }1 1
    

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74. MainActivity.kt
    val db = // ...
    db.transaction {4
    it.delete("users", "first_name = ?", arrayOf("jake"))
    }3
    Databases.kt
    inline fun SQLiteDatabase.transaction(body: SQLiteDatabase.() -> Unit) {
    beginTransaction()
    try {
    body(this)F
    setTransactionSuccessful()
    } finally {
    endTransaction()
    }2
    }1 1
    SQLiteDatabase.() -> Unit
    

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75. MainActivity.kt
    val db = // ...
    db.transaction {4
    it.delete("users", "first_name = ?", arrayOf("jake"))
    }3
    Databases.kt
    inline fun SQLiteDatabase.transaction(body: SQLiteDatabase.() -> Unit) {
    beginTransaction()
    try {
    body()
    setTransactionSuccessful()
    } finally {
    endTransaction()
    }2
    }1 1
    SQLiteDatabase.() -> Unit
    body()F
    

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76. it.
    MainActivity.kt
    val db = // ...
    db.transaction {4
    delete("users", "first_name = ?", arrayOf("jake"))
    }3
    Databases.kt
    inline fun SQLiteDatabase.transaction(body: SQLiteDatabase.() -> Unit) {
    beginTransaction()
    try {
    body()
    setTransactionSuccessful()
    } finally {
    endTransaction()
    }2
    }1 1
    delete
    SQLiteDatabase.() -> Unit
    body()F
    

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77. MainActivity.kt
    val db = // ...
    db.transaction {4
    delete("users", "first_name = ?", arrayOf("jake"))G
    }3
    Databases.kt
    inline fun SQLiteDatabase.transaction(body: SQLiteDatabase.() -> Unit) {
    beginTransaction()
    try {
    body()
    setTransactionSuccessful()
    } finally {
    endTransaction()
    }2
    }1 1
    

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78. MainActivity.kt
    = // ...
    "jake"
    Databases.kt
    inline fun SQLiteDatabase.transaction(body: SQLiteDatabase.() -> Unit) {
    beginTransaction()
    try {
    body()
    setTransactionSuccessful()
    } finally {
    endTransaction()
    }2
    }1 1
    class UserPersistence(private val db: SQLiteDatabase) {
    fun deleteByFirstName(name: String) {
    db.transaction {
    delete("users", "first_name = ?", arrayOf(name))G
    }3
    }
    }
    UserPersistence.kt
    

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79. MainActivity.kt
    = // ...
    "jake"
    Databases.kt
    inline fun SQLiteDatabase.transaction(body: SQLiteDatabase.() -> Unit) {
    beginTransaction()
    try {
    body()
    setTransactionSuccessful()
    } finally {
    endTransaction()
    }2
    }1 1
    class UserPersistence(private val db: SQLiteDatabase) {
    fun deleteByFirstName(name: String) {
    db.transaction {
    delete("users", "first_name = ?", arrayOf(name))G
    }3
    }
    }
    UserPersistence.kt
    

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80. class UserPersistence(private val db: SQLiteDatabase) {
    fun deleteByFirstName(name: String) {
    db.transaction {
    delete("users", "first_name = ?", arrayOf(name))G
    }3
    }2
    }1
    UserPersistence.kt
    

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81. class UserPersistence(private val db: SQLiteDatabase) {
    private val deleteByFirstName = db.compileStatement(
    "DELETE FROM users WHERE first_name = ?")
    fun deleteByFirstName(name: String) {
    db.transaction {
    deleteByFirstName.bindString(1, name)
    deleteByFirstName.execute()
    }3
    }2
    }1
    UserPersistence.kt
    delete(" ", " , arrayOf( ))G
    

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82. sssssssssssss
    class UserPersistence(private val db: SQLiteDatabase) {
    private val deleteByFirstName = db.compileStatement(
    "DELETE FROM users WHERE first_name = ?")
    fun deleteByFirstName(name: String) {
    db.transaction {
    deleteByFirstName.bindString(1, name)
    deleteByFirstName.execute()
    }3
    }2
    }1
    UserPersistence.kt
    

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83. sssssssssssss
    class UserPersistence(private val db: SQLiteDatabase) {
    private val deleteByFirstName by lazy {
    db.compileStatement("DELETE FROM users WHERE first_name = ?")
    }
    fun deleteByFirstName(name: String) {
    db.transaction {
    deleteByFirstName.bindString(1, name)
    deleteByFirstName.execute()
    }3
    }2
    }1
    UserPersistence.kt
    

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84. sssssssssssss
    class UserPersistence(private val db: SQLiteDatabase) {
    private val deleteByFirstName by lazy {
    db.compileStatement("DELETE FROM users WHERE first_name = ?")
    }X
    fun deleteByFirstName(name: String) {
    db.transaction {
    deleteByFirstName.bindString(1, name)
    deleteByFirstName.execute()
    }3
    }2
    }1
    UserPersistence.kt
    

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85. private val deleteByFirstName by lazy {
    db.compileStatement("DELETE FROM users WHERE first_name = ?")
    }X
    

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86. private val deleteByFirstName by lazy {
    db.compileStatement("DELETE FROM users WHERE first_name = ?")
    }X
    private val name by Delegates.observable("jane") { old, new, prop ->
    println("Name changed from $old to $new")
    }
    

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87. private val deleteByFirstName by lazy {
    db.compileStatement("DELETE FROM users WHERE first_name = ?")
    }X
    private val name by Delegates.observable("jane") { old, new, prop ->
    println("Name changed from $old to $new")
    }
    private val address by Delegates.notNull()
    

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88. private val deleteByFirstName by lazy {
    db.compileStatement("DELETE FROM users WHERE first_name = ?")
    }X
    private val name by Delegates.observable("jane") { old, new, prop ->
    println("Name changed from $old to $new")
    }
    private val address by Delegates.notNull()
    private val nameView by bindView(R.id.name)
    

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89. private val deleteByFirstName by lazy {
    db.compileStatement("DELETE FROM users WHERE first_name = ?")
    }X
    private val name by Delegates.observable("jane") { old, new, prop ->
    println("Name changed from $old to $new")
    }
    private val address by Delegates.notNull()
    private val nameView by bindView(R.id.name)
    

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90. class MyListener : TransitionListener {
    override fun onTransitionEnd(transition: Transition) {
    }
    override fun onTransitionResume(transition: Transition) {
    }
    override fun onTransitionPause(transition: Transition) {
    }
    override fun onTransitionCancel(transition: Transition) {
    }
    override fun onTransitionStart(transition: Transition) {
    }Y
    }X
    

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91. class MyListener : TransitionListener {
    override fun onTransitionStart(transition: Transition) {
    }Y
    }X
    

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92. class MyListener : TransitionListener {
    override fun onTransitionStart(transition: Transition) {
    }Y
    }X
    object EmptyTransitionListener : TransitionListener {
    override fun onTransitionEnd(transition: Transition) {}
    override fun onTransitionResume(transition: Transition) {}
    override fun onTransitionPause(transition: Transition) {}
    override fun onTransitionCancel(transition: Transition) {}
    override fun onTransitionStart(transition: Transition) {}
    }
    

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93. class MyListener : TransitionListener {
    override fun onTransitionStart(transition: Transition) {
    }Y
    }X
    object EmptyTransitionListener : TransitionListener {
    override fun onTransitionEnd(transition: Transition) {}
    override fun onTransitionResume(transition: Transition) {}
    override fun onTransitionPause(transition: Transition) {}
    override fun onTransitionCancel(transition: Transition) {}
    override fun onTransitionStart(transition: Transition) {}
    }
    

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94. class MyListener : TransitionListener {T
    override fun onTransitionStart(transition: Transition) {
    }Y
    }X
    object EmptyTransitionListener : TransitionListener {
    override fun onTransitionEnd(transition: Transition) {}
    override fun onTransitionResume(transition: Transition) {}
    override fun onTransitionPause(transition: Transition) {}
    override fun onTransitionCancel(transition: Transition) {}
    override fun onTransitionStart(transition: Transition) {}
    }G
    

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95. class MyListener : TransitionListener by EmptyTransitionListener {T
    override fun onTransitionStart(transition: Transition) {
    }Y
    }X
    object EmptyTransitionListener : TransitionListener {
    override fun onTransitionEnd(transition: Transition) {}
    override fun onTransitionResume(transition: Transition) {}
    override fun onTransitionPause(transition: Transition) {}
    override fun onTransitionCancel(transition: Transition) {}
    override fun onTransitionStart(transition: Transition) {}
    }G
    

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96. class MyListener : TransitionListener by EmptyTransitionListener {T
    override fun onTransitionStart(transition: Transition) {
    }Y
    }X
    object EmptyTransitionListener : TransitionListener {
    override fun onTransitionEnd(transition: Transition) {}
    override fun onTransitionResume(transition: Transition) {}
    override fun onTransitionPause(transition: Transition) {}
    override fun onTransitionCancel(transition: Transition) {}
    override fun onTransitionStart(transition: Transition) {}
    }G
    

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97. class PaymentRobot {
    fun amount(value: Long) {
    // TODO Espresso interactions
    }
    fun recipient(value: String) {
    // TODO Espresso interactions
    }
    fun send() {
    // TODO Espresso interactions
    }
    }
    PaymentRobot.kt
    

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98. @Test fun sendMoney() {
    PaymentRobot().apply {
    amount(4_00)
    recipient("foo@example.com")
    send()
    }
    }
    PaymentTest.kt
    

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99. class PaymentRobot {
    fun amount(value: Long) {
    // TODO Espresso interactions
    }
    fun recipient(value: String) {
    // TODO Espresso interactions
    }
    fun send() {
    // TODO Espresso interactions
    }
    }
    PaymentRobot.kt
    

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100. class PaymentRobot {
     fun amount(value: Long) {
     // TODO Espresso interactions
     }
     fun recipient(value: String) {
     // TODO Espresso interactions
     }
     fun send() {
     // TODO Espresso interactions
     }
     }
     PaymentRobot.kt
     fun payment(body: PaymentRobot.() -> Unit) = PaymentRobot().apply(body)
     

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101. class PaymentRobot {
     fun amount(value: Long) {
     // TODO Espresso interactions
     }
     fun recipient(value: String) {
     // TODO Espresso interactions
     }
     fun send() {
     // TODO Espresso interactions
     }
     }
     PaymentRobot.kt
     fun payment(body: PaymentRobot.() -> Unit) = PaymentRobot().apply(body)
     

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102. @Test fun sendMoney() {
     PaymentRobot().apply {T
     amount(4_00)
     recipient("foo@example.com")
     send()
     }T
     }G
     PaymentTest.kt
     p
     

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103. @Test fun sendMoney() {
     payment {T
     amount(4_00)
     recipient("foo@example.com")
     send()
     }T
     }G
     PaymentTest.kt
     

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104. sealed class Payloads {
     }G
     

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105. sealed class Payloads {
     data class Favorite(val favorited: Boolean) : Payloads()
     }G
     

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106. sealed class Payloads {
     data class Favorite(val favorited: Boolean) : Payloads()
     data class Retweet(val retweeted: Boolean) : Payloads()
     }G
     

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107. sealed class Payloads {
     data class Favorite(val favorited: Boolean) : Payloads()
     data class Retweet(val retweeted: Boolean) : Payloads()
     data class CountUpdate(
     val favorites: Long,
     val retweets: Long,
     val replies: Long) : Payloads()
     }G
     

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108. override fun onBindViewHolder(holder: TweetViewHolder,
     position: Int, payloads: List) {
     }1
     

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109. override fun onBindViewHolder(holder: TweetViewHolder,
     position: Int, payloads: List) {
     payloads.forEach {
     }2
     }1
     

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110. override fun onBindViewHolder(holder: TweetViewHolder,
     position: Int, payloads: List) {
     payloads.forEach {
     when (it) {
     }3
     }2
     }1
     

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111. override fun onBindViewHolder(holder: TweetViewHolder,
     position: Int, payloads: List) {
     payloads.forEach {
     when (it) {
     is Favorite -> holder.favoriteIcon.isActivated = it.favorited
     }3
     }2
     }1
     

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112. override fun onBindViewHolder(holder: TweetViewHolder,
     position: Int, payloads: List) {
     payloads.forEach {
     when (it) {
     is Favorite -> holder.favoriteIcon.isActivated = it.favorited
     }3
     }2
     }1
     

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113. override fun onBindViewHolder(holder: TweetViewHolder,
     position: Int, payloads: List) {
     payloads.forEach {
     when (it) {
     is Favorite -> holder.favoriteIcon.isActivated = it.favorited
     }3
     }2
     }1
     sealed class Payloads {
     data class Favorite(val favorited: Boolean) : Payloads()
     data class Retweet(val retweeted: Boolean) : Payloads()
     data class CountUpdate(
     val favorites: Long,
     val retweets: Long,
     val replies: Long) : Payloads()
     }G
     

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114. override fun onBindViewHolder(holder: TweetViewHolder,
     position: Int, payloads: List) {
     payloads.forEach {
     when (it) {
     is Favorite -> holder.favoriteIcon.isActivated = it.favorited
     }3
     }2
     }1
     

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115. override fun onBindViewHolder(holder: TweetViewHolder,
     position: Int, payloads: List) {
     payloads.forEach {
     when (it) {
     is Favorite -> holder.favoriteIcon.isActivated = it.favorited
     is Retweet -> holder.retweetIcon.isActivated = it.retweeted
     }3
     }2
     }1
     

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116. override fun onBindViewHolder(holder: TweetViewHolder,
     position: Int, payloads: List) {
     payloads.forEach {
     when (it) {
     is Favorite -> holder.favoriteIcon.isActivated = it.favorited
     is Retweet -> holder.retweetIcon.isActivated = it.retweeted
     is CountUpdate -> {
     holder.apply {
     favoriteCount.text = it.favorites.toString()
     retweetCount.text = it.retweets.toString()
     replyCount.text = it.replies.toString()
     }5
     }4
     }3
     }2
     }1
     

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117. View Slide

118. It takes great salesmanship to
     convince a customer to buy
     something from you that isn't
     built or isn't finished.
     Fred Wilson
     

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119. View Slide

120. View Slide

121. Step 3
     Step 2
     Step 1
     

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122. Step 1 Step 3
     You
     Step 2
     

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123. Step 3
     Management
     Step 2
     Step 1
     

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124. Team
     Step 3
     Step 2
     Step 1
     

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125. You
     Get excited.
     

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126. Never doubt that a
     small group of
     thoughtful, committed
     citizens can change
     the world; indeed,

     it's the only thing 

     that ever has.
     Margaret Mead (Def. not talking about tech)
     

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127. Be enthusiastic
     

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128. Adoption is work. If you want it, you need to earn it.
     

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129. Management
     Be persuasive.
     

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130. I call it my billion-
     dollar mistake.
     Sir Charles Antony Richard Hoare
     

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131. One of the most feared
     expressions in modern
     times is 'The computer
     is down.'
     Norman Ralph Augustine
     

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132. View Slide

133. Jake Wharton
     @JakeWharton
     Type systems are a form of tests. I declare an expected
     type and the tests (aka compiler) validates the actual ones.
     6:43 PM - 11 Jan 2017
     74
     Follow
     16
     

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134. View Slide

135. Team
     Do the work.
     

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136. Ellen Shapiro @designatednerd
     My style: “I’m the idiot who went down the rabbit hole first,
     and I’m here to tell you which path leads to fluffy bunnies vs.
     angry moles.”
     14 Mar
     Ellen Shapiro
     @designatednerd
     My favorite bit of any talk I give is talking about the dumb
     shit I did so the audience doesn’t do it. Makes the hair
     pulled out worth it.
     4:56 PM - 14 Mar 2017
     1
     Follow
     

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137. Define success
     

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138. View Slide

139. View Slide

140. http://blog.danlew.net/
     

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141. On-boarding
     should be a first
     class citizen
     

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142. Show up
     

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143. View Slide

144. What’s next?
     Kotlin documentation and koans
     https://kotlinlang.org/
     Android Kotlin documentation
     https://developer.android.com/kotlin/index.html
     Kotlin In Action
     Dimitry Jemerov, Svetlana Isakova
     

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145. +Christina Lee
     @RunChristinaRun
     #KotlinIsHere
     Thank you!
     +Jake Wharton
     @JakeWharton
     

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146. View Slide