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.

1. unctions in PHP Part 1: Writing Your Own Functions ƒ
2. <?php ! $hash = array( 'username' => 'john', 'food' => 'bacon', ); ! echo http_build_query($hash); ! // The above code would output... username=john&food=bacon
3. <?php ! $hash = array( 'username' => 'john', 'food' => 'bacon', ); ! echo http_build_query($hash); ! // The above code would output... username=john&food=bacon
4. function sum($foo, $bar) { return $foo + $bar; }
5. function sum($foo, $bar) { return $foo + $bar; } echo sum(2, 2);
6. function sum($foo, $bar) { return $foo + $bar; } echo sum(2, 2); 4
7. function sum($foo, $bar) { return $foo + $bar; } echo sum(2, 2); 4 echo sum(16, 8);
8. function sum($foo, $bar) { return $foo + $bar; } echo sum(2, 2); 4 echo sum(16, 8); 24
9. Blocks of Reusable Code
10. Blocks of Reusable Code Easy to read and digest
11. Blocks of Reusable Code Easy to read and digest Easier to Maintain
12. Anatomy! of Functions
13. function announce_sum($foo, $bar) { $sum = $foo + $bar; return $sum; } Function Keyword
14. function announce_sum($foo, $bar) { $sum = $foo + $bar; return $sum; } Name
15. function announce_sum($foo, $bar) { $sum = $foo + $bar; return $sum; } Arguments
16. function announce_sum($foo, $bar) { $sum = $foo + $bar; return $sum; } Body
17. function announce_sum($foo, $bar) { $sum = $foo + $bar; return $sum; } Return
19. Given
20. Given Expect
21. Given Expect Behavior
22. Given! List of all Users
23. Given! List of all Users Expect! New list of Users whose name starts with J
24. Given! List of all Users Users With J Names Expect! New list of Users whose name starts with J
25. function users_with_j_names($users) { $filtered = array(); ! // ... do some work ... return $filtered; }
26. function users_with_j_names($users) { $filtered = array(); ! // ... do some work ... return $filtered; }
27. 1. Well Named Describes what the function does! not how it does it
28. function users_with_j_names($users) { $filtered = array(); ! // ... do some work ... return $filtered; }
29. foreach ($users as $user) { if (0 === strpos($user['name'], 'J')) { $filtered[] = $user; } } function users_with_j_names($users) { $filtered = array(); return $filtered; }
30. foreach ($users as $user) { if (0 === strpos($user['name'], 'J')) { $filtered[] = $user; } } function users_with_j_names($users) { $filtered = array(); return $filtered; }
31. foreach ($users as $user) { if (0 === strpos($user['name'], 'J')) { $filtered[] = $user; } } function users_with_j_names($users) { $filtered = array(); return $filtered; }
32. Users With J Names Users With K Names Users With L Names Users With M Names Users With N Names Users With O Names
33. Given! List of all Users One Letter ! Expect! New list of Users whose name starts with One Letter
34. Given! List of all Users One Letter ! Expect! New list of Users whose name starts with One Letter Users Name Begins With
35. function users_name_begins_with($users, $letter) { $filtered = array(); ! foreach ($users as $user) { if (0 === strpos($user['name'], $letter)) { $filtered[] = $user; } } return $filtered; }
36. function users_name_begins_with($users, $letter) { $filtered = array(); ! foreach ($users as $user) { if (0 === strpos($user['name'], $letter)) { $filtered[] = $user; } } return $filtered; }
37. 2. Change vs Same Separate what changes! from what stays the same
38. 2. Change vs Same Separate what changes! from what stays the same Arguments
39. 2. Change vs Same Separate what changes! from what stays the same Behavior Arguments
40. function users_name_begins_with($users, $letter) { $filtered = array(); ! foreach ($users as $user) { if (0 === strpos($user['name'], $letter)) { $filtered[] = $user; } } return $filtered; }
41. function users_name_begins_with($users, $letter) { $filtered = array(); ! foreach ($users as $user) { if (0 === strpos($user['name'], $letter)) { $filtered[] = $user; } } return $filtered; } 1. Well Named
42. function users_name_begins_with($users, $letter) { $filtered = array(); ! foreach ($users as $user) { if (0 === strpos($user['name'], $letter)) { $filtered[] = $user; } } return $filtered; } 1. Well Named 2. Change vs Same
43. 3. One Return Type Return the same value type! given any input
44. Integer! Float! Boolean! String! Array! Object 0 1 2 3! 0.0 1.0 3.14! true false! "hello" ""! array() array('john', 'eric', 'dan')! DateTime User 3. One Return Type
45. function users_name_begins_with($users, $letter) { $filtered = array(); ! foreach ($users as $user) { if (0 === strpos($user['name'], $letter)) { $filtered[] = $user; } } ! return $filtered; }
46. function users_name_begins_with($users, $letter) { $filtered = array(); ! foreach ($users as $user) { if (0 === strpos($user['name'], $letter)) { $filtered[] = $user; } } ! return $filtered; }
47. function users_name_begins_with($users, $letter) { $filtered = array(); ! foreach ($users as $user) { if (0 === strpos($user['name'], $letter)) { $filtered[] = $user; } } ! return $filtered; } 3. One Return Type
48. Variable Scope http://www.flickr.com/photos/pedrovezini/5747037907
49. <?php $a = 1; // global scope ! function test() { echo $a; // reference to function scope } ! test(); Global Scope
50. <?php $a = 1; // global scope ! function test($b) { echo $b; // reference to function scope } ! test($a); Local Variable Scope
51. <?php $a = 1; // global scope ! function test($b) { echo $b; // reference to function scope } ! test($a); Local Variable Scope
52. <?php $a = 1; // global scope ! function test() { global $a; echo $a; // reference to function scope } ! test($a);
53. <?php $a = 1; // global scope ! function test() { global $a; echo $a; // reference to function scope } ! test($a);
54. <?php $a = 1; // global scope ! function test() { global $a; echo $a; // reference to function scope } ! test($a); 1
55. <?php $a = 1; // global scope ! function test() { global $a; echo $a; // reference to function scope } ! test($a); 1 Avoid using global
56. <?php $a = 1; // global scope ! function test() { global $a; echo $a; // reference to function scope } ! test($a); 1 Avoid using global and its friend $GLOBAL
57. $_GET! $_POST! $_SERVER! $_FILES Superglobals $_COOKIE! $_SESSION! $_REQUEST! $_ENV
58. Imagine you're @ http://domain.com/hello.php?name=john <?php ! function test() { echo $_GET['name']; } ! test(); Super Global Scope
59. Imagine you're @ http://domain.com/hello.php?name=john <?php ! function test() { echo $_GET['name']; } ! test(); Super Global Scope
60. Imagine you're @ http://domain.com/hello.php?name=john <?php ! function test() { echo $_GET['name']; } ! test(); Super Global Scope john
61. 4. Control In and Out Control what goes in! and what comes out
62. 4. Control In and Out Control what goes in! and what comes out Arguments
63. 4. Control In and Out Control what goes in! and what comes out Return Arguments
64. function users_name_begins_with($users, $letter) { $filtered = array(); ! foreach ($users as $user) { if (0 === strpos($user['name'], $letter)) { $filtered[] = $user; } } return $filtered; }
65. function users_name_begins_with($users, $letter) { $filtered = array(); ! foreach ($users as $user) { if (0 === strpos($user['name'], $letter)) { $filtered[] = $user; } } return $filtered; } 4. Control In and Out
66. function users_name_begins_with($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
67. combine to make Larger Programs Small Programs
74. BUILD SMALL PROGRAMS
75. unctions in PHP Part 1: Writing Your Own Functions ƒ