Functions in PHP: Part 1 - Writing Your Own Functions

John Kary discusses 4 guidelines that if followed will result in clear, focused functions that are easy to read, reason about and reuse. Examples are shown in PHP.

Transcript

1. unctions in PHP
   Part 1: Writing Your Own Functions
   ƒ
   

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2. !
   $hash = array(
   'username' => 'john',
   'food' => 'bacon',
   );
   !
   echo http_build_query($hash);
   !
   // The above code would output...
   username=john&food=bacon
   

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3. !
   $hash = array(
   'username' => 'john',
   'food' => 'bacon',
   );
   !
   echo http_build_query($hash);
   !
   // The above code would output...
   username=john&food=bacon
   

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4. function sum($foo, $bar) {
   return $foo + $bar;
   }
   

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5. function sum($foo, $bar) {
   return $foo + $bar;
   }
   echo sum(2, 2);
   

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6. function sum($foo, $bar) {
   return $foo + $bar;
   }
   echo sum(2, 2);
   4
   

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7. function sum($foo, $bar) {
   return $foo + $bar;
   }
   echo sum(2, 2);
   4
   echo sum(16, 8);
   

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8. function sum($foo, $bar) {
   return $foo + $bar;
   }
   echo sum(2, 2);
   4
   echo sum(16, 8);
   24
   

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9. Blocks of Reusable Code
   

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10. Blocks of Reusable Code
    Easy to read and digest
    

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11. Blocks of Reusable Code
    Easy to read and digest
    Easier to Maintain
    

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12. Anatomy!
    of Functions
    

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13. function announce_sum($foo, $bar) {
    $sum = $foo + $bar;
    return $sum;
    }
    Function Keyword
    

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14. function announce_sum($foo, $bar) {
    $sum = $foo + $bar;
    return $sum;
    }
    Name
    

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15. function announce_sum($foo, $bar) {
    $sum = $foo + $bar;
    return $sum;
    }
    Arguments
    

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16. function announce_sum($foo, $bar) {
    $sum = $foo + $bar;
    return $sum;
    }
    Body
    

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17. function announce_sum($foo, $bar) {
    $sum = $foo + $bar;
    return $sum;
    }
    Return
    

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19. Given
    

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20. Given
    Expect
    

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21. Given
    Expect
    Behavior
    

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22. Given!
    List of all Users
    

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23. Given!
    List of all Users
    Expect!
    New list of Users whose name starts with J
    

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24. Given!
    List of all Users
    Users With J Names
    Expect!
    New list of Users whose name starts with J
    

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25. function users_with_j_names($users) {
    $filtered = array();
    !
    // ... do some work ...
    return $filtered;
    }
    

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26. function users_with_j_names($users) {
    $filtered = array();
    !
    // ... do some work ...
    return $filtered;
    }
    

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27. 1. Well Named
    Describes what the function does!
    not how it does it
    

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28. function users_with_j_names($users) {
    $filtered = array();
    !
    // ... do some work ...
    return $filtered;
    }
    

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29. foreach ($users as $user) {
    if (0 === strpos($user['name'], 'J')) {
    $filtered[] = $user;
    }
    }
    function users_with_j_names($users) {
    $filtered = array();
    return $filtered;
    }
    

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30. foreach ($users as $user) {
    if (0 === strpos($user['name'], 'J')) {
    $filtered[] = $user;
    }
    }
    function users_with_j_names($users) {
    $filtered = array();
    return $filtered;
    }
    

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31. foreach ($users as $user) {
    if (0 === strpos($user['name'], 'J')) {
    $filtered[] = $user;
    }
    }
    function users_with_j_names($users) {
    $filtered = array();
    return $filtered;
    }
    

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32. Users With J Names
    Users With K Names
    Users With L Names
    Users With M Names
    Users With N Names
    Users With O Names
    

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33. Given!
    List of all Users
    One Letter
    !
    Expect!
    New list of Users whose name starts with One Letter
    

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34. Given!
    List of all Users
    One Letter
    !
    Expect!
    New list of Users whose name starts with One Letter
    Users Name Begins With
    

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35. function users_name_begins_with($users, $letter) {
    $filtered = array();
    !
    foreach ($users as $user) {
    if (0 === strpos($user['name'], $letter)) {
    $filtered[] = $user;
    }
    }
    return $filtered;
    }
    

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36. function users_name_begins_with($users, $letter) {
    $filtered = array();
    !
    foreach ($users as $user) {
    if (0 === strpos($user['name'], $letter)) {
    $filtered[] = $user;
    }
    }
    return $filtered;
    }
    

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37. 2. Change vs Same
    Separate what changes!
    from what stays the same
    

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38. 2. Change vs Same
    Separate what changes!
    from what stays the same
    Arguments
    

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39. 2. Change vs Same
    Separate what changes!
    from what stays the same
    Behavior
    Arguments
    

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40. function users_name_begins_with($users, $letter) {
    $filtered = array();
    !
    foreach ($users as $user) {
    if (0 === strpos($user['name'], $letter)) {
    $filtered[] = $user;
    }
    }
    return $filtered;
    }
    

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41. function users_name_begins_with($users, $letter) {
    $filtered = array();
    !
    foreach ($users as $user) {
    if (0 === strpos($user['name'], $letter)) {
    $filtered[] = $user;
    }
    }
    return $filtered;
    }
    1. Well Named
    

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42. function users_name_begins_with($users, $letter) {
    $filtered = array();
    !
    foreach ($users as $user) {
    if (0 === strpos($user['name'], $letter)) {
    $filtered[] = $user;
    }
    }
    return $filtered;
    }
    1. Well Named
    2. Change vs Same
    

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43. 3. One Return Type
    Return the same value type!
    given any input
    

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44. Integer!
    Float!
    Boolean!
    String!
    Array!
    Object
    0 1 2 3!
    0.0 1.0 3.14!
    true false!
    "hello" ""!
    array() array('john', 'eric', 'dan')!
    DateTime User
    3. One Return Type
    

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45. function users_name_begins_with($users, $letter) {
    $filtered = array();
    !
    foreach ($users as $user) {
    if (0 === strpos($user['name'], $letter)) {
    $filtered[] = $user;
    }
    }
    !
    return $filtered;
    }
    

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46. function users_name_begins_with($users, $letter) {
    $filtered = array();
    !
    foreach ($users as $user) {
    if (0 === strpos($user['name'], $letter)) {
    $filtered[] = $user;
    }
    }
    !
    return $filtered;
    }
    

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47. function users_name_begins_with($users, $letter) {
    $filtered = array();
    !
    foreach ($users as $user) {
    if (0 === strpos($user['name'], $letter)) {
    $filtered[] = $user;
    }
    }
    !
    return $filtered;
    }
    3. One Return Type
    

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48. Variable Scope
    http://www.flickr.com/photos/pedrovezini/5747037907
    

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49. $a = 1; // global scope
    !
    function test() {
    echo $a; // reference to function scope
    }
    !
    test();
    Global Scope
    

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50. $a = 1; // global scope
    !
    function test($b) {
    echo $b; // reference to function scope
    }
    !
    test($a);
    Local Variable Scope
    

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51. $a = 1; // global scope
    !
    function test($b) {
    echo $b; // reference to function scope
    }
    !
    test($a);
    Local Variable Scope
    

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52. $a = 1; // global scope
    !
    function test() {
    global $a;
    echo $a; // reference to function scope
    }
    !
    test($a);
    

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53. $a = 1; // global scope
    !
    function test() {
    global $a;
    echo $a; // reference to function scope
    }
    !
    test($a);
    

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54. $a = 1; // global scope
    !
    function test() {
    global $a;
    echo $a; // reference to function scope
    }
    !
    test($a);
    1
    

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55. $a = 1; // global scope
    !
    function test() {
    global $a;
    echo $a; // reference to function scope
    }
    !
    test($a);
    1
    Avoid using global
    

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56. $a = 1; // global scope
    !
    function test() {
    global $a;
    echo $a; // reference to function scope
    }
    !
    test($a);
    1
    Avoid using global
    and its friend $GLOBAL
    

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57. $_GET!
    $_POST!
    $_SERVER!
    $_FILES
    Superglobals
    $_COOKIE!
    $_SESSION!
    $_REQUEST!
    $_ENV
    

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58. Imagine you're @ http://domain.com/hello.php?name=john
    !
    function test() {
    echo $_GET['name'];
    }
    !
    test();
    Super Global Scope
    

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59. Imagine you're @ http://domain.com/hello.php?name=john
    !
    function test() {
    echo $_GET['name'];
    }
    !
    test();
    Super Global Scope
    

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60. Imagine you're @ http://domain.com/hello.php?name=john
    !
    function test() {
    echo $_GET['name'];
    }
    !
    test();
    Super Global Scope
    john
    

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61. 4. Control In and Out
    Control what goes in!
    and what comes out
    

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62. 4. Control In and Out
    Control what goes in!
    and what comes out
    Arguments
    

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63. 4. Control In and Out
    Control what goes in!
    and what comes out
    Return
    Arguments
    

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64. function users_name_begins_with($users, $letter) {
    $filtered = array();
    !
    foreach ($users as $user) {
    if (0 === strpos($user['name'], $letter)) {
    $filtered[] = $user;
    }
    }
    return $filtered;
    }
    

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65. function users_name_begins_with($users, $letter) {
    $filtered = array();
    !
    foreach ($users as $user) {
    if (0 === strpos($user['name'], $letter)) {
    $filtered[] = $user;
    }
    }
    return $filtered;
    }
    4. Control In and Out
    

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66. function users_name_begins_with($users, $letter) {
    $filtered = array();
    !
    foreach ($users as $user) {
    if (0 === strpos($user['name'], $letter)) {
    $filtered[] = $user;
    }
    }
    return $filtered;
    } 4. Control In and Out
    3. One Return Type
    1. Well Named
    2. Change vs Same
    

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67. combine to make
    Larger Programs
    Small Programs
    

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74. BUILD SMALL PROGRAMS
    

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75. unctions in PHP
    Part 1: Writing Your Own Functions
    ƒ
    

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