Modern PHP Cheatsheet

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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 (PHP 8.0 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:

Modern PHP cheatsheet

Notions

Function default parameter value

You can set default value to your function parameters:

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

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

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

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

$b = myFunction($undefined); // PHP Warning:  Undefined variable $undefined
// $b = null

Type declaration

With Type declaration you can specify the expected data type for a property that will be enforce at runtime. It supports many types like scalar types (int, string, bool, and float) but also array, iterable, object, stdClass, etc.

You can set a type to a function's parameter:

function myFunction(int $param)
{
    return $param;
}
$a = myFunction(10);
// $a = 10
$b = myFunction('foo'); // TypeError: myFunction(): Argument #1 ($param) must be of type int, string given

You can set a return type to a function:

function myFunction() : int
{
    return 'foo';
}
$a = myFunction(); // TypeError: myFunction(): Return value must be of type int, string returned

When a function should not return something, you can use the type "void":

function myFunction() : void
{
    return 'foo';
}
// PHP Fatal error:  A void function must not return a value

You cannot return null either:

function myFunction() : void
{
    return null;
}
// PHP Fatal error:  A void function must not return a value

However, using return to exit the function is valid:

function myFunction() : void
{
    return;
}
$a = myFunction();
// $a = null

Class property

You can set a return type to a class property:

Class Foo()
{
    public int $bar;
}
$f = new Foo();
$f->bar = 'baz'; // TypeError: Cannot assign string to property Foo::$bar of type int

Union type

You can use a “union type” that accepts values of multiple different types, rather than a single one:

function myFunction(string|int|array $param) : string|int|array
{
    return $param;
}

It also works with class property:

Class Foo()
{
    public string|int|array $bar;
}

Nullable type

When a parameter has no type, it can accept null value:

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

But as soon as a parameter has a type, it won't accept null value anymore and you'll get an error:

function myFunction(string $param)
{
    return $param;
}
$a = myFunction(null); // TypeError: myFunction(): Argument #1 ($param) must be of type string, null given

If a function has a return type, it won't accept null value either:

function myFunction() : string
{
    return null;
}
$a = myFunction(); // TypeError: myFunction(): Return value must be of type string, null returned

You can make a type declaration explicitly nullable:

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

or with a union type:

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

It also works with return type:

function myFunction(?string $param) : ?string
{
    return $param;
}
// or
function myFunction(string|null $param) : string|null
{
    return $param;
}

But void cannot be nullable:

function myFunction() : ?void
{
   // some code
} 
// PHP Fatal error:  Void type cannot be nullable

function myFunction() : void|null
{
   // some code
}
// PHP Fatal error:  Void type cannot be nullable

You can set a nullable type to a class property:

Class Foo()
{
    public int|null $bar;
}
$f = new Foo();
$f->bar = null;
$a = $f->bar;
// $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 since PHP 7.1, the shorthand syntax:

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

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

You can skip elements:

list(, , $c) = $array;

// $c = 'baz'

Or since PHP 7.1, 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 is equivalent to:

$a = null;
$b = isset($a) ? $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

You can chain null coalescing multiple times:

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

Elvis operator

It should not be confused with the shorthand ternary operator (aka the elvis operator), which was introduced in PHP 5.3:

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

// $b = 'fallback'

The shorthand ternary operator is equivalent to:

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

Result between null coalescing and elvis operator can be similar, but also different for some specific values:

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

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()

Null Coalescing Assignment operator

You can set a default value to a property when it is null:

$a = null;
$a = $a ?? 'foo';
// $a = 'foo'

Since PHP 7.4, you can use the null coalescing assignment operator to do the same:

$a = null;
$a ??= 'foo';
// $a = 'foo'

Nullsafe operator

When trying to read a property or calling a method on null, you'll get a warning and an error:

$a = null;
$b = $a->foo; // PHP Warning:  Attempt to read property "foo" on null
// $b = null

$c = $a->foo(); // PHP Error:  Call to a member function foo() on null

With the nullsafe operator, you can do both without warning nor error:

$a = null;
$b = $a?->foo;
// $b = null
$c = $a?->foo();
// $c = null

You can chain multiple nullsafe operators:

$a = null;
$b = $a?->foo?->bar;
// $b = null
$c = $a?->foo()?->bar();
// $c = null

An expression is short-circuited from the first null-safe operator that encounters null:

$a = null;
$b = $a?->foo->bar->baz();
// $b = null

Nullsafe operator has no effect if the target is not null:

$a = 'foo';
$b = $a?->bar; // PHP Warning:  Attempt to read property "bar" on string
// $b = null
$c = $a?->baz(); // PHP Error:  Call to a member function baz() on string

Nullsafe operator can't handle arrays properly but still can have some effect:

$a = [];
$b = $a['foo']->bar;
// PHP Warning:  Undefined array key "foo"
// PHP Warning:  Attempt to read property "bar" on null
// $b = null

$c = $a['foo']?->bar; // PHP Warning:  Undefined array key "foo"
// $c = null

$d = $a['foo']->bar();
// PHP Warning:  Undefined array key "foo"
// PHP Error:  Call to a member function bar() on null

$e = $a['foo']?->bar(); // PHP Warning:  Undefined array key "foo"
// $e = null

You cannot use the nullsafe operator to write, it is read only:

$a = null;
$a?->foo = 'bar'; // PHP Fatal error:  Can't use nullsafe operator in write context

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)
{ 
   // some code
}
// PHP Fatal error: Only the last parameter can be variadic

You can have only one variadic parameter:

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

It can't have a default value:

function countParameters(string $param, string ...$options = [])
{
   // some code
}
// 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

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']

Unpacking only works with arrays (or objects inplementing Traversable interface). If you try to unpack any other value, such as 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']

arthurkirkosa / modern-php-cheatsheet

Modern PHP Cheatsheet

Introduction

Motivation

Complementary Resources

Table of Contents

Notions

Function default parameter value

Type declaration

Class property

Union type

Nullable type

Destructuring arrays

Indexed array

Associative array

Null Coalescing

Elvis operator

Null coalescing on array

Null coalescing on object

Object's attribute

Object's method

Chained method

Null Coalescing Assignment operator

Nullsafe operator

Spread operator

Variadic parameter

Argument unpacking

Array unpacking

Indexed array

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