Modern Php Cheatsheet

If you like this content, you can ping me or follow me on Twitter 👍

Introduction

Motivation

This document is a cheatsheet for Php you will frequently encounter in modern projects and most contemporary sample code.

This guide is not intended to teach you Php from the ground up, but to help developers with basic knowledge who may struggle to get familiar with modern codebases (or let's say to learn Laravel or Symfony for instance) because of the new Php concepts and features introduced over the years.

Note: Concepts introduced here are based on the most recent version of php available (Php8 at the time of the last update)

Complementary Resources

When you struggle to understand a notion, I suggest you look for answers on the following resources:

• Stitcher's blog
• PHP.Watch
• PHP The Right Way
• StackOverflow

Table of Contents

• Modern Php cheatsheet
  • Introduction
    • Motivation
    • Complementary resources
  • Table of contents
  • Notions
    • Function default parameter value
    • Destructuring arrays
    • Null Coalescing
    • Spread operator

Notions

Function default parameter value

You can set default value to your function parameters:

function myFunction(string $param = 'foo') {
    return $param;
}
$a = myFunction();
// $a = 'foo'

$b = myFunction('bar');
// $a = 'bar'

But if you send null or an undefined property, default value won't be used:

function myFunction(string $param = 'foo') {
    return $param;
}
$a = myFunction(null);
// $a = null

$b = myFunction($undefined);
// $a = null

Destructuring arrays

You can destructure arrays to pull out several elements into separate variables.

Indexed array

Considering an indexed array like :

$array = ['foo', 'bar', 'baz'];

You can destruct it using the list syntax:

list($a, $b, $c) = $array;

// $a = 'foo'
// $b = 'bar'
// $c = 'baz'

Or the shorthand syntax:

[$a, $b, $c] = $array;

// $a = 'foo'
// $b = 'bar'
// $c = 'baz'

You can skip elements:

list(, , $c) = $array;

// $c = 'baz'

Or the shorthand syntax:

[, , $c] = $array;

// $c = 'baz'

When you try to destruct an index that doesn't exist in the given array, you'll get a warning:

list($a, $b, $c, $d) = $array; // PHP Warning:  Undefined array key 3

// $a = 'foo'
// $b = 'bar'
// $c = 'baz'
// $d = null;

Associative array

Considering an associative array (string-keyed) like :

$array = [
    'foo' => 'value1',
    'bar' => 'value2',
    'baz' => 'value3',
];

Previous list syntax won't work with an associative array, and you'll get a warning:

list($a, $b, $c) = $array; // PHP Warning:  Undefined array key 0 ...

// $a = null
// $b = null
// $c = null

But since php 7.1.0 (~ dec 2016), you can destruct it with another syntax based on keys:

list('foo' => $a, 'bar' => $b, 'baz' => $c) = $array;

// $a = 'value1'
// $b = 'value2'
// $c = 'value3'

Or the shorthand syntax:

['foo' => $a, 'bar' => $b, 'baz' => $c] = $array;

// $a = 'value1'
// $b = 'value2'
// $c = 'value3'

You can also destruct only a portion of the array (The order doesn't matter):

['baz' => $c, 'foo' => $a] = $array;

// $a = 'value1'
// $c = 'value3'

When you try to destruct a key that doesn't exist in the given array, you'll get a warning:

list('moe' => $d) = $array; // PHP Warning:  Undefined array key "moe"

// $d = null

Null Coalescing

Since php 7.0 (~ dec 2015), you can use the null coalescing operator to provide a fallback when a property is null with no error nor warning:

$a = null;
$b = $a ?? 'fallback';

// $b = 'fallback'

It also works when property is undefined:

$a = $undefined ?? 'fallback';

// $a = 'fallback'

Every other value of the property won't trigger the fallback:

'' ?? 'fallback'; // ''
0 ?? 'fallback'; // 0
false ?? 'fallback'; // false

Null coalescing on array

If array key exists, then fallback isn't triggered:

$a = ['foo' => 'bar'];
$b = $a['foo'] ?? 'fallback';

// $b = 'bar'

But when array doesn't exist, fallback is triggered with no error nor warning:

$a = null;
$b = $a['foo'] ?? 'fallback';

// $b = 'fallback'

Or array property is undefined, fallback is triggered with no error nor warning:

$b = $undefined['foo'] ?? 'fallback';

// $b = 'fallback'

When array exist but key can't be found in the given array, fallback is triggered with no error nor warning:

$a = [];
$b = $a['foo'] ?? 'fallback';

// $b = 'fallback'

It also works with indexed arrays:

$a = ['foo'];

// reminder: $a[0] = 'foo'

$b = $a[1] ?? 'fallback';

// $b = 'fallback'

It also works with nested arrays. If nested array key exists, then fallback isn't triggered:

$a = [
   'foo' => [
      'bar' => 'baz'
   ]
];
$b = $a['foo']['bar'] ?? 'fallback';

// $b = 'baz'

But when nested key can't be found in the given array, fallback is triggered with no error nor warning:

$a = [
   'foo' => [
      'bar' => 'baz'
   ]
];
$b = $a['foo']['qux'] ?? 'fallback';

// $b = 'fallback'

Null coalescing on object

You can also use null coalescing operator with object.

Object's attribute

If object's attribute exists, then fallback isn't triggered:

$a = (object)[
    'foo' => 'bar'
];
$b = $a->foo ?? 'fallback';

// $b = 'bar'

But when object's attribute can't be found, fallback is triggered with no error nor warning:

$a = (object)[
    'foo' => 'bar'
];
$b = $a->baz ?? 'fallback';

// $b = 'fallback'

Object's method

You can also use the null coalescing operator on call to an object's method. If the given method exists, then fallback isn't triggered:

class Foo
{
    public function bar() {
        return 'baz';
    }
}

$a = new Foo();
$b = $a->bar() ?? 'fallback';

// $b = 'baz'

But when object's method returns null, fallback is triggered with no error nor warning:

class Foo
{
    public function bar() {
        return null;
    }
}

$a = new Foo();
$b = $a->bar() ?? 'fallback';

// $b = 'fallback'

If object's method can't be found, null coalescing won't work and you'll get an error:

class Foo
{
    public function bar() {
        return 'baz';
    }
}

$a = new Foo();
$b = $a->baz() ?? 'fallback'; // PHP Error:  Call to undefined method baz()

Chained method

When using chained methods on object and an intermediary element can't be found, null coalescing won't work and you'll get an error:

class Foo
{
    public function bar() {
        return (object)[];
    }
}

$a = new Foo();
$b = $a->bar()->baz() ?? 'fallback'; // PHP Error:  Call to undefined method baz()

Spread operator

Variadic parameter

Since php 5.6 (~ aug 2014), you can add a variadic parameter to any function that let you use an argument lists with variable-length:

function countParameters(string $param, string ...$options) : int {

    foreach ($options as $option) {
        // you can iterate on $options
    }
 
    return 1 + count($options);
}

countParameters('foo'); // 1
countParameters('foo', 'bar'); // 2
countParameters('foo', 'bar', 'baz'); // 3

Variadic parameter should always be the last parameter declared:

function countParameters(string ...$options, string $param) { ... }
// PHP Fatal error: Only the last parameter can be variadic

You can have only one variadic parameter:

function countParameters(string ...$options, string ...$moreOptions) { ... }
// PHP Fatal error: Only the last parameter can be variadic

It can't have a default value:

function countParameters(string $param, string ...$options = []) { ... }
// PHP Parse error: Variadic parameter cannot have a default value

When not typed, it accepts any value:

function countParameters(string $param, ...$options) : int {
    return 1 + count($options);
}

countParameters('foo', null, [], true); // 4

When typed, you have to use properly typed values:

function countParameters(string $param, string ...$options) : int {
    return 1 + count($options);
}

countParameters('foo', null);
// TypeError: countParameters(): Argument #2 must be of type string, null given

countParameters('foo', []);
// TypeError: countParameters(): Argument #2 must be of type string, array given

Argument unpacking

Since php 5.6 (~ aug 2014), arrays and traversable objects can be unpacked into argument lists when calling functions by using the spread operator:

function add(int $a, int $b, int $c) : int {
    return $a + $b + $c;
}
$array = [2, 3];
$r = add(1, ...$array);

// $r = 6

The given array can have more elements than needed:

function add(int $a, int $b, int $c) : int {
    return $a + $b + $c;
}
$array = [2, 3, 4, 5];
$r = add(1, ...$array);

// $r = 6

The given array can't have lesser elements than needed:

function add(int $a, int $b, int $c) : int {
    return $a + $b + $c;
}
$array = [2];
$r = add(1, ...$array); // TypeError: Too few arguments to function add(), 2 passed

Except when some function arguments have a default value:

function add(int $a, int $b, int $c = 0) : int {
    return $a + $b + $c;
}
$array = [2];
$r = add(1, ...$array);
// $r = 3

If an argument is typed and the passed value does not match the given type, you'll get an error:

function add(int $a, int $b, int $c) : int {
    return $a + $b + $c;
}
$array = ['foo', 'bar'];
$r = add(1, ...$array); // TypeError: add(): Argument #2 ($b) must be of type int, string given

It is possible to use an associative array, but keys should match arguments names

function add(int $a, int $b, int $c) : int {
    return $a + $b + $c;
}
$array = [
    "b" => 2,
    "c" => 3
];
$r = add(1, ...$array);
// $r = 6

Order of the elements in the associative array doesn't matter:

function add(int $a, int $b, int $c) : int {
    return $a + $b + $c;
}
$array = [
    "c" => 3,
    "b" => 2,
];
$r = add(1, ...$array);
// $r = 6

If a key doesn't match an argument's name, you'll get an error:

function add(int $a, int $b, int $c) : int {
    return $a + $b + $c;
}
$array = [
    "b" => 2,
    "c" => 3,
    "d" => 4,
];
$r = add(1, ...$array); // PHP Error:  Unknown named parameter $d

Array unpacking

Indexed array

When you want to merge multiple arrays, you generally use array_merge:

$array1 = ['baz'];
$array2 = ['foo', 'bar'];

$array3 = array_merge($array1,$array2);
// $array3 = ['baz', 'foo', 'bar']

But since php 7.4 (~ nov 2019), you can unpack indexed arrays, with spread operator:

$array1 = ['foo', 'bar'];
$array2 = ['baz', ...$array1];
// $array2 = ['baz', 'foo', 'bar']

Elements will be merged in the order they are passed:

$array1 = ['foo', 'bar'];
$array2 = ['baz', ...$array1, "qux"];
// $array2 = ['baz', 'foo', 'bar', "qux"]

It doesn't do any deduplication:

$array1 = ['foo', 'bar'];
$array2 = ['foo', ...$array1];
// $array2 = ['foo', 'foo', 'bar']

You can unpack multiple arrays at once:

$array1 = ['foo', 'bar'];
$array2 = ['baz'];
$array3 = [ ...$array1, ...$array2];
// $array3 = ['foo', 'bar', 'baz']

You can unpack the same array multiple times:

$array1 = ['foo', 'bar'];
$array2 = [ ...$array1, ...$array1];
// $array2 = ['foo', 'bar', 'foo', 'bar']

You can unpack an empty array with no error nor warning:

$array1 = [];
$array2 = ['foo', ...$array1];
// $array2 = ['foo']

You can unpack an array that has not been previously stored in a property:

$array1 = [...['foo', 'bar'], 'baz'];
// $array1 = ['foo', 'bar', 'baz']

If you try to unpack an array valued with null, you'll get an error:

$array1 = null;
$array2 = ['foo', ...$array1]; // PHP Error:  Only arrays and Traversables can be unpacked

You can unpack the result of a function/method:

function getArray() : array {
  return ['foo', 'bar'];
}

$array = [...getArray(), 'baz']; 
// $array = ['foo', 'bar', 'baz']

Associative array

Since php 8.1 (~ nov 2021), you can unpack associative array (string-keyed):

$array1 = ['foo' => 'bar'];
$array2 = [
   'baz' => 'qux', 
   ...$array1
];
// $array2 = ['foo' => 'bar', 'baz' => 'qux']

@todo: same key ? empty array ? etc