Kotlin: The Good Parts (DevFest 2017)

Una charla sobre Kotlin para Android, donde recorremos un poco la sintaxis, los "por qué" y algunas de las características que hacen de este lenguaje ideal para ser utilizado en Android.

Esta charla fue parte del DevFest 2017 organizada por el GDGNeuquen el 11/11/2017

Transcript

1. KOTLIN
 THE GOOD PARTS RICARDO MARKIEWICZ
2. STATICALLY TYPED PROGRAMMING LANGUAGE FOR MODERN MULTIPLATFORM APPLICATIONS http://kotlinlang.org/ KOTLIN
3. 100% INTEROPERABLE WITH JAVA™ AND ANDROID™ http://kotlinlang.org/ KOTLIN
4. ¡NOW OFFICIAL ON ANDROID! http://kotlinlang.org/ KOTLIN
6. TEXT ¿POR QUÉ KOTLIN? ▸ Restricciones y problemas de Java ▸ No se pueden extender tipos de la plataforma (Util hell) ▸ NPE Madness ▸ Threading / Mutability ▸ Too verbose ▸ Problemas de diseño de APIs de Android
7. TEXT ¿POR QUÉ KOTLIN? ▸ Problemas de diseño de APIs de Android ▸ Inheritance party ▸ NULL por todos lados ▸ Ceremonias
8. KOTLIN SINTAXIS fun mult(a: Int, b:Int): Int { 
 return a + b 
 }}
9. KOTLIN SINTAXIS fun mult(a: Int, b:Int): Int { 
 return a + b 
 }}
10. KOTLIN SINTAXIS fun mult(a: Int, b:Int): Int { 
 return a + b 
 } 

11. KOTLIN SINTAXIS fun mult(a: Int, b:Int) = a + b

12. KOTLIN SINTAXIS fun main(args: Array<String>) { 
 println("Args: $args") 
 }
13. KOTLIN SINTAXIS fun main(args: Array<String>) { 
 println("Args: $args") 
 }
14. KOTLIN SINTAXIS fun main(args: Array<String>) { 
 println("Args: $args") 
 }
15. KOTLIN SINTAXIS val charla = "Kotlin" 
 val asistente: List<String> = ArrayList() 
 var tarea: String? = null
16. KOTLIN SINTAXIS val charla = "Kotlin" 
 val asistente: List<String> = ArrayList() 
 var tarea: String? = null
17. KOTLIN SINTAXIS val charla = "Kotlin" 
 val asistente: List<String> = ArrayList() 
 var tarea: String? = null
18. KOTLIN SINTAXIS val charla = "Kotlin" 
 val asistente: List<String> = ArrayList() 
 var tarea: String? = null
19. KOTLIN SINTAXIS val charla = "Kotlin" 
 val asistente: List<String> = ArrayList() 
 var tarea: String? = null
20. EXTENSION FUNCTIONS
21. KOTLIN EXTENSION FUNCTIONS // DateUtil.java 
 class DateUtil { 
 public static boolean isWeekend(Date date) { 
 int dayOfWeek = date.getDay(); 
 return dayOfWeek == 0 || dayOfWeek == 6 
 }}
 } 
 
 // Somefile.java 
 Date date = new Date() 
 if (DateUtil.isWeekend(date)) { 
 }}
22. KOTLIN EXTENSION FUNCTIONS // DateUtil.kt 
 public static boolean isWeekend(Date date) { 
 int dayOfWeek = date.getDay(); 
 return dayOfWeek == 0 || dayOfWeek == 6 
 }}
 
 // Somefile.java 
 Date date = new Date() 
 if (DateUtil.isWeekend(date)) { 
 
 }}
23. KOTLIN EXTENSION FUNCTIONS // DateUtil.kt 
 fun isWeekend(Date date): Boolean { 
 int dayOfWeek = date.getDay(); 
 return dayOfWeek == 0 || dayOfWeek == 6 
 }}
 
 // Somefile.java 
 Date date = new Date() 
 if (DateUtil.isWeekend(date)) { 
 
 }}
24. KOTLIN EXTENSION FUNCTIONS // DateUtil.kt 
 fun Date.isWeekend(): Boolean { 
 int dayOfWeek = getDay(); 
 return dayOfWeek == 0 || dayOfWeek == 6 
 }}
 
 // Somefile.java 
 Date date = new Date() 
 if (DateUtil.isWeekend(date)) { 
 
 }}
25. KOTLIN EXTENSION FUNCTIONS // DateUtil.kt 
 fun Date.isWeekend(): Boolean { 
 int dayOfWeek = getDay(); 
 return dayOfWeek == 0 || dayOfWeek == 6 
 }}
 
 // Somefile.java 
 Date date = new Date() 
 if (DateUtil.isWeekend(date)) { 
 
 }}
26. KOTLIN EXTENSION FUNCTIONS // DateUtil.kt 
 fun Date.isWeekend(): Boolean { 
 int dayOfWeek = getDay(); 
 return dayOfWeek == 0 || dayOfWeek == 6 
 }}
 
 // Somefile.java 
 Date date = new Date() 
 if (DateUtil.isWeekend(date)) { 
 
 }}
27. KOTLIN EXTENSION FUNCTIONS // DateUtil.kt 
 fun Date.isWeekend(): Boolean { 
 int dayOfWeek = getDay(); 
 return dayOfWeek == 0 || dayOfWeek == 6 
 }}
 
 // Somefile.java 
 Date date = new Date() 
 if (DateUtil.isWeekend(date)) { 
 
 }}
28. KOTLIN EXTENSION FUNCTIONS // DateUtil.kt 
 fun Date.isWeekend(): Boolean { 
 int dayOfWeek = getDay(); 
 return dayOfWeek == 0 || dayOfWeek == 6 
 }}
 
 // Somefile.java 
 Date date = new Date() 
 if (date.isWeekend()) { 
 
 }}
29. KOTLIN EXTENSION FUNCTIONS // DateUtil.kt 
 fun Date.isWeekend(): Boolean { 
 int dayOfWeek = day; 
 return dayOfWeek == 0 || dayOfWeek == 6 
 }}
 
 // Somefile.java 
 Date date = new Date() 
 if (date.isWeekend()) { 
 
 }}
30. KOTLIN EXTENSION FUNCTIONS // DateUtil.kt 
 fun Date.isWeekend(): Boolean {
 return day == 0 || day == 6 
 }}
 
 // Somefile.java 
 Date date = new Date() 
 if (date.isWeekend()) { 
 
 }}
31. KOTLIN EXTENSION FUNCTIONS // DateUtil.kt 
 fun Date.isWeekend() = day == 0 || day == 6
 
 // Somefile.java 
 Date date = new Date() 
 if (date.isWeekend()) { 
 
 }}
32. KOTLIN EXTENSION FUNCTIONS // DateUtil.kt 
 fun Date.isWeekend() = day == 0 || day == 6
 
 // Somefile.java 
 Date date = new Date() 
 if (date.isWeekend()) { 
 
 }} // DateUtil.java 
 class DateUtil { 
 public static boolean isWeekend(Date date) { 
 int dayOfWeek = date.getDay(); 
 return dayOfWeek == 0 || dayOfWeek == 6 
 } 
 } 
 
 // Somefile.java 
 Date date = new Date() 
 if (DateUtil.isWeekend(date)) { 
 
 } 

33. FUNCTION EXPRESSIONS
34. KOTLIN FUNCTION EXPRESSIONS ▸ { it.toString() } ▸ { x, y -> x + y } ▸ { x: Int, y: Int -> x * y } ▸ val sum: (Int, Int) -> Int = { x, y -> x + y } ▸ val mult = { x: Int, y: Int -> x * y } ▸ sum(2, 4)
35. KOTLIN FUNCTION EXPRESSIONS ▸ val notEmpty: (String) -> Boolean = { !it.isEmpty() } ▸ val fourOrMore: (String) -> Boolean = { it.length() >= 4 } ▸ val someCrazyValidation: (String) -> Boolean = { heavyProcess(it) }
36. HIGHER-ORDER FUNCTIONS
37. KOTLIN HIGHER-ORDER FUNCTIONS A higher-order function is a function that takes functions as parameters, or returns a function
38. KOTLIN HIGHER-ORDER FUNCTIONS val names = listOf("Ricardo", "Martin", "Roberto", "Carlos") 
 
 fun namesThatStartWith(...): List<String> { 
 
 } 
 
 val withR = namesThatStartWith(names, ...) 

39. KOTLIN HIGHER-ORDER FUNCTIONS val names = listOf("Ricardo", "Martin", "Roberto", "Carlos") 
 
 fun namesThatStartWith(list:List<String>, …): List<String> { 
 
 } 
 
 val withR = namesThatStartWith(names, ...) 

40. KOTLIN HIGHER-ORDER FUNCTIONS val names = listOf("Ricardo", "Martin", "Roberto", "Carlos") 
 
 fun namesThatStartWith(list:List<String>, matcher: (String) -> Boolean): List<String> { 
 
 } 
 
 val withR = namesThatStartWith(names, ...) 

41. KOTLIN HIGHER-ORDER FUNCTIONS val names = listOf("Ricardo", "Martin", "Roberto", "Carlos") 
 
 fun namesThatStartWith(list:List<String>, matcher: (String) -> Boolean): List<String> { 
 
 } 
 
 val withR = namesThatStartWith(names, ...) 

42. KOTLIN HIGHER-ORDER FUNCTIONS val names = listOf("Ricardo", "Martin", "Roberto", "Carlos") 
 
 fun namesThatStartWith(list:List<String>, matcher: (String) -> Boolean): List<String> { 
 
 } 
 
 val withR = namesThatStartWith(names, ...) 

43. KOTLIN HIGHER-ORDER FUNCTIONS val names = listOf("Ricardo", "Martin", "Roberto", "Carlos") 
 
 fun namesThatStartWith(list:List<String>, matcher: (String) -> Boolean): List<String> { 
 } 
 
 val withR = namesThatStartWith(names, { it.matches("^R") })

44. KOTLIN HIGHER-ORDER FUNCTIONS val names = listOf("Ricardo", "Martin", "Roberto", "Carlos") 
 
 fun namesThatStartWith(list:List<String>, matcher: (String) -> Boolean): List<String> { 
 } 
 
 val withR = namesThatStartWith(names) { it.matches("^R") }

45. KOTLIN HIGHER-ORDER FUNCTIONS val names = listOf("Ricardo", "Martin", "Roberto", "Carlos") 
 
 fun namesThatStartWith(list:List<String>, matcher: (String) -> Boolean): List<String> { 
 } 
 
 val withR = namesThatStartWith(names) { it.matches("^R") }

46. KOTLIN HIGHER-ORDER FUNCTIONS val names = listOf("Ricardo", "Martin", "Roberto", "Carlos") 
 
 fun namesThatStartWith(list:List<String, matcher: (String) -> Boolean): List<String> { 
 } 
 
 val withR = namesThatStartWith(names) { it.matches("^R") }

47. KOTLIN HIGHER-ORDER FUNCTIONS val names = listOf("Ricardo", "Martin", "Roberto", "Carlos") 
 
 fun namesThatStartWith(list:List<String, matcher: (String) -> Boolean): List<String> { 
 var tmp = ArrayList() 
 list.forEach { 
 if (matches(it)) { 
 tmp.append(it) 
 } 
 } 
 return tmp 
 } 
 val withR = namesThatStartWith(names) { it.matches("^R") }

48. KOTLIN HIGHER-ORDER FUNCTIONS val names = listOf("Ricardo", "Martin", "Roberto", "Carlos") 
 
 fun namesThatStartWith(list:List<String, matcher: (String) -> Boolean): List<String> { 
 var tmp = ArrayList() 
 list.forEach { 
 if (matches(it)) { 
 tmp.append(it) 
 } 
 } 
 return tmp 
 } 
 val withR = namesThatStartWith(names) { it.matches("^R") }

49. KOTLIN HIGHER-ORDER FUNCTIONS val names = listOf("Ricardo", "Martin", "Roberto", "Carlos") 
 
 fun namesThatStartWith(list:List<String, matcher: (String) -> Boolean): List<String> { 
 var tmp = ArrayList() 
 list.forEach { 
 if (matches(it)) { 
 tmp.append(it) 
 } 
 } 
 return tmp 
 } 
 val withR = namesThatStartWith(names) { it.matches("^R") }

51. HIGH-ORDER FUNCTIONS + EXTENSION FUNCTIONS
52. KOTLIN HIGH-ORDER FUNCTIONS + EXTENSION FUNCTIONS fun <T> List<T>.filter(predicate: (T) -> Boolean): List<T> { 
 // ... 
 } 
 
 val names = listOf("Ricardo", "Martin", "Roberto", "Carlos") 
 
 val withR = names.filter { it.matches("/^R/") }
53. KOTLIN HIGH-ORDER FUNCTIONS + EXTENSION FUNCTIONS fun <T> List<T>.filter(predicate: (T) -> Boolean): List<T> { 
 // ... 
 } 
 
 val names = listOf("Ricardo", "Martin", "Roberto", "Carlos") 
 
 val withR = names.filter { it.matches("/^R/") }
54. KOTLIN HIGH-ORDER FUNCTIONS + EXTENSION FUNCTIONS fun <T> List<T>.filter(predicate: (T) -> Boolean): List<T> { 
 // ... 
 } 
 
 val names = listOf("Ricardo", "Martin", "Roberto", "Carlos") 
 
 val withR = names.filter { it.matches("/^R/") }
55. KOTLIN HIGH-ORDER FUNCTIONS + EXTENSION FUNCTIONS fun <T> List<T>.filter(predicate: (T) -> Boolean): List<T> { 
 // ... 
 } 
 
 val names = listOf("Ricardo", "Martin", "Roberto", "Carlos") 
 
 val withR = names.filter { it.matches("/^R/") }
56. KOTLIN HIGH-ORDER FUNCTIONS + EXTENSION FUNCTIONS fun <T> List<T>.filter(predicate: (T) -> Boolean): List<T> { 
 // ... 
 } 
 
 val names = listOf("Ricardo", "Martin", "Roberto", "Carlos") 
 
 val withR = names.filter { it.matches("/^R/") }
57. KOTLIN HIGH-ORDER FUNCTIONS + EXTENSION FUNCTIONS fun <T> List<T>.filter(predicate: (T) -> Boolean): List<T> { 
 // ... 
 } 
 
 val names = listOf("Ricardo", "Martin", "Roberto", "Carlos") 
 
 val withR = names.filter { it.matches("/^R/") }
58. KOTLIN HIGH-ORDER FUNCTIONS + EXTENSION FUNCTIONS fun <T> List<T>.filter(predicate: (T) -> Boolean): List<T> { 
 // ... 
 } 
 
 val names = listOf("Ricardo", "Martin", "Roberto", "Carlos") 
 
 val withR = names.filter { it.matches("/^R/") }
59. DATA CLASSES
60. KOTLIN DATA CLASS ▸ Clase que guarda datos ▸ Inmutable ▸ Clases comunes: Pair / Triple
61. KOTLIN DATA CLASS data class User(val name: String, val age: Int) 

62. KOTLIN DATA CLASS data class User(val name: String, val age: Int) 

63. KOTLIN DATA CLASS data class User(val name: String, val age: Int) 

64. KOTLIN DATA CLASS data class User(val name: String, val age: Int) 

65. KOTLIN DATA CLASS data class User(val name: String, val age: Int) 
 
 val me = User("Ricardo", 38)
66. KOTLIN DATA CLASS data class User(val name: String, val age: Int) 
 
 val me = User("Ricardo", 38) 
 
 val (name, age) = me
67. KOTLIN DATA CLASS data class User(val name: String, val age: Int) 
 
 val me = User("Ricardo", 38) 
 
 val (name, age) = me 
 
 fun Float.toFrac(): Pair { 
 // ... 
 } 
 
 val n = 1.5 
 val (num, den) = n.toFrac() 

68. KOTLIN DATA CLASS data class User(val name: String, val age: Int) 
 
 val me = User("Ricardo", 38) 
 
 val (name, age) = me 
 
 fun Float.toFrac(): Pair { 
 // ... 
 } 
 
 val n = 1.5 
 val (num, den) = n.toFrac() 

69. KOTLIN DATA CLASS data class User(val name: String, val age: Int) 
 
 val me = User("Ricardo", 38) 
 
 val (name, age) = me 
 
 fun Float.toFrac(): Pair { 
 // ... 
 } 
 
 val n = 1.5 
 val (num, den) = n.toFrac() 

70. ¡THE GOOD PARTS!
72. KOTLIN REDUCE BOILERPLATE class LoginActivity : AppCompatActivity() { 
 internal var emailView: TextView? = null 
 internal var passwordView: TextView? = null 
 
 override fun onCreate(savedInstanceState: Bundle?) { 
 super.onCreate(savedInstanceState) 
 setContentView(R.layout.activity_login) 
 
 emailView = (TextView) findViewById(R.id.email) 
 passwordView = (TextView) findViewById(R.id.password) 
 
 if (emailView != null) { 
 emailView.setSomeImportantStuff(...) 
 }} 
 }}
 }}
73. KOTLIN REDUCE BOILERPLATE inline fun <reified T : View> Activity.find(id: Int): T = findViewById(id) as T 
 
 class LoginActivity : AppCompatActivity() { 
 internal var emailView: TextView? = null 
 internal var passwordView: TextView? = null 
 
 override fun onCreate(savedInstanceState: Bundle?) { 
 super.onCreate(savedInstanceState) 
 setContentView(R.layout.activity_login) 
 
 emailView = (TextView) findViewById(R.id.email) 
 passwordView = (TextView) findViewById(R.id.password) 
 
 if (emailView != null) { 
 emailView.setSomeImportantStuff(...) 
 }}
 }}

74. KOTLIN REDUCE BOILERPLATE inline fun <reified T : View> Activity.find(id: Int): T = findViewById(id) as T 
 
 class LoginActivity : AppCompatActivity() { 
 internal var emailView: TextView? = null 
 internal var passwordView: TextView? = null 
 
 override fun onCreate(savedInstanceState: Bundle?) { 
 super.onCreate(savedInstanceState) 
 setContentView(R.layout.activity_login) 
 
 emailView = (TextView) findViewById(R.id.email) 
 passwordView = (TextView) findViewById(R.id.password) 
 
 if (emailView != null) { 
 emailView.setSomeImportantStuff(...) 
 }}
 }}

75. KOTLIN REDUCE BOILERPLATE inline fun <reified T : View> Activity.find(id: Int): T = findViewById(id) as T 
 
 class LoginActivity : AppCompatActivity() { 
 internal var emailView: TextView? = null 
 internal var passwordView: TextView? = null 
 
 override fun onCreate(savedInstanceState: Bundle?) { 
 super.onCreate(savedInstanceState) 
 setContentView(R.layout.activity_login) 
 
 emailView = (TextView) findViewById(R.id.email) 
 passwordView = (TextView) findViewById(R.id.password) 
 
 if (emailView != null) { 
 emailView.setSomeImportantStuff(...) 
 }}
 }}

76. KOTLIN REDUCE BOILERPLATE inline fun <reified T : View> Activity.find(id: Int): T = findViewById(id) as T 
 
 class LoginActivity : AppCompatActivity() { 
 internal var emailView: TextView? = null 
 internal var passwordView: TextView? = null 
 
 override fun onCreate(savedInstanceState: Bundle?) { 
 super.onCreate(savedInstanceState) 
 setContentView(R.layout.activity_login) 
 
 emailView = find<TextView>(R.id.email) 
 passwordView = find<TextView>(R.id.password) 
 
 if (emailView != null) { 
 emailView.setSomeImportantStuff(...) 
 }} 
 }}

77. KOTLIN REDUCE BOILERPLATE inline fun <reified T : View> Activity.find(id: Int): T = findViewById(id) as T 
 
 class LoginActivity : AppCompatActivity() { 
 internal val emailView: TextView = find<TextView>(R.id.email) 
 internal val passwordView: TextView = find<TextView>(R.id.password) 
 
 override fun onCreate(savedInstanceState: Bundle?) { 
 super.onCreate(savedInstanceState) 
 setContentView(R.layout.activity_login) 
 
 if (emailView != null) { 
 emailView.setSomeImportantStuff(...) 
 }} 
 }}
 }}

78. KOTLIN REDUCE BOILERPLATE inline fun <reified T : View> Activity.find(id: Int): T = findViewById(id) as T 
 
 class LoginActivity : AppCompatActivity() { 
 internal val emailView: TextView = find<TextView>(R.id.email) 
 internal val passwordView: TextView = find<TextView>(R.id.password) 
 
 override fun onCreate(savedInstanceState: Bundle?) { 
 super.onCreate(savedInstanceState) 
 setContentView(R.layout.activity_login) 
 
 if (emailView != null) { 
 emailView.setSomeImportantStuff(...) 
 }} 
 }}
 }}
79. KOTLIN REDUCE BOILERPLATE inline fun <reified T : View> Activity.find(id: Int): T = findViewById(id) as T 
 
 class LoginActivity : AppCompatActivity() { 
 internal val emailView: TextView = find<TextView>(R.id.email) 
 internal val passwordView: TextView = find<TextView>(R.id.password) 
 
 override fun onCreate(savedInstanceState: Bundle?) { 
 super.onCreate(savedInstanceState) 
 setContentView(R.layout.activity_login) 
 
 if (emailView != null) { 
 emailView.setSomeImportantStuff(...) 
 }} 
 }}
 }}
80. KOTLIN REDUCE BOILERPLATE inline fun <reified T : View> Activity.find(id: Int): T = findViewById(id) as T 
 
 class LoginActivity : AppCompatActivity() { 
 internal val emailView by lazy { find<TextView>(R.id.email) } 
 internal val passwordView by lazy { find<TextView>(R.id.password) } 
 
 override fun onCreate(savedInstanceState: Bundle?) { 
 super.onCreate(savedInstanceState) 
 setContentView(R.layout.activity_login) 
 
 if (emailView != null) { 
 emailView.setSomeImportantStuff(...) 
 }} 
 }}
 }}
81. KOTLIN REDUCE BOILERPLATE inline fun <reified T : View> Activity.find(id: Int): T = findViewById(id) as T 
 
 class LoginActivity : AppCompatActivity() { 
 internal val emailView by lazy { find<TextView>(R.id.email) } 
 internal val passwordView by lazy { find<TextView>(R.id.password) } 
 
 override fun onCreate(savedInstanceState: Bundle?) { 
 super.onCreate(savedInstanceState) 
 setContentView(R.layout.activity_login) 
 
 emailView.setSomeImportantStuff(...) 
 }}
 }}
82. KOTLIN REDUCE ERRORS db.beginTransaction() 
 try { 
 db.delete("users", "first_name = ?", new String[] { "Ricardo" }); 
 } finally { 
 db.endTransaction(); 
 }
83. KOTLIN REDUCE ERRORS db.beginTransaction() 
 try { 
 db.delete("users", "first_name = ?", new String[] { "Ricardo" }); db.setTransactionSuccess();
 } finally { 
 db.endTransaction(); 
 }
84. KOTLIN REDUCE ERRORS fun SQLiteDatabase.inTransaction(func: () -> Unit) { 
 beginTransaction() 
 try { 
 func() 
 setTransactionSuccess() 
 } finally { 
 endTransaction(); 
 } 
 }
85. KOTLIN REDUCE ERRORS fun SQLiteDatabase.inTransaction(func: () -> Unit) { 
 beginTransaction() 
 try { 
 func() 
 setTransactionSuccess() 
 } finally { 
 endTransaction(); 
 } 
 } 
 
 db.inTransaction { 
 }
86. KOTLIN REDUCE ERRORS fun SQLiteDatabase.inTransaction(func: () -> Unit) { 
 beginTransaction() 
 try { 
 func() 
 setTransactionSuccess() 
 } finally { 
 endTransaction(); 
 } 
 } 
 
 db.inTransaction { 
 db.delete("users", "first_name = ?", arrayOf("Ricardo")) 
 }
87. KOTLIN REDUCE ERRORS fun SQLiteDatabase.inTransaction(func: (SQLiteDatabase) -> Unit) { 
 beginTransaction() 
 try { 
 func() 
 setTransactionSuccess() 
 } finally { 
 endTransaction(); 
 } 
 } 
 
 db.inTransaction { 
 db.delete("users", "first_name = ?", arrayOf("Ricardo")) 
 }
88. KOTLIN REDUCE ERRORS fun SQLiteDatabase.inTransaction(func: (SQLiteDatabase) -> Unit) { 
 beginTransaction() 
 try { 
 func(this) 
 setTransactionSuccess() 
 } finally { 
 endTransaction(); 
 } 
 } 
 
 db.inTransaction { 
 db.delete("users", "first_name = ?", arrayOf("Ricardo")) 
 }
89. KOTLIN REDUCE ERRORS fun SQLiteDatabase.inTransaction(func: (SQLiteDatabase) -> Unit) { 
 beginTransaction() 
 try { 
 func(this) 
 setTransactionSuccess() 
 } finally { 
 endTransaction(); 
 } 
 } 
 
 db.inTransaction { 
 it.delete(“users", "first_name = ?", arrayOf("Ricardo")) 
 }
90. KOTLIN REDUCE ERRORS fun SQLiteDatabase.inTransaction(func: SQLiteDatabase.() -> Unit) { 
 beginTransaction() 
 try { 
 func(this) 
 setTransactionSuccess() 
 } finally { 
 endTransaction(); 
 } 
 } 
 
 db.inTransaction { 
 it.delete(“users", "first_name = ?", arrayOf("Ricardo")) 
 }
91. KOTLIN REDUCE ERRORS fun SQLiteDatabase.inTransaction(func: SQLiteDatabase.() -> Unit) { 
 beginTransaction() 
 try { 
 this.func() 
 setTransactionSuccess() 
 } finally { 
 endTransaction(); 
 } 
 } 
 
 db.inTransaction { 
 it.delete(“users", "first_name = ?", arrayOf("Ricardo")) 
 }
92. KOTLIN REDUCE ERRORS fun SQLiteDatabase.inTransaction(func: SQLiteDatabase.() -> Unit) { 
 beginTransaction() 
 try { 
 func() 
 setTransactionSuccess() 
 } finally { 
 endTransaction(); 
 } 
 } 
 
 db.inTransaction { 
 it.delete(“users", "first_name = ?", arrayOf("Ricardo")) 
 }
93. KOTLIN REDUCE ERRORS fun SQLiteDatabase.inTransaction(func: SQLiteDatabase.() -> Unit) { 
 beginTransaction() 
 try { 
 func() 
 setTransactionSuccess() 
 } finally { 
 endTransaction(); 
 } 
 } 
 
 db.inTransaction { 
 delete(“users", "first_name = ?", arrayOf("Ricardo")) 
 }
94. KOTLIN THE GOOD PARTS inline fun notification(context: Context, func: Notification.Builder.() -> Unit): Notification { 
 val builder = Notification.Builder(context) 
 builder.func() 
 return builder.build() 
 } 
 
 val n = notification(context) { 
 setContentTitle("Kotlin") 
 setSubText("The Good parts :)") 
 }
95. KOTLIN THE GOOD PARTS val email:: TextView = // ... 
 
 email.setVisibility(View.GONE) 
 email.setVisibility(View.VISIBLE)
96. KOTLIN THE GOOD PARTS val email:: TextView = // ... 
 
 email.hide() 
 email.show()
97. KOTLIN THE GOOD PARTS val email:: TextView = // ... 
 
 email.hide() 
 email.show() 
 
 inline fun TextView.hide() { visibility = View.GONE } 
 inline fun TextView.show() { visibility = View.VISIBLE }
98. ¡MUCHAS GRACIAS! RICARDO MARKIEWICZ - @GAZERIA