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 8.3 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:

Recent PHP releases

Version	Release date
PHP 8.3	December 2023
PHP 8.2	December 2022
PHP 8.1	November 2021
PHP 8.0	November 2020
PHP 7.4	November 2019
PHP 7.3	December 2018
PHP 7.2	November 2017
PHP 7.1	December 2016
PHP 7.0	December 2015

More infos on php.net.

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

Trailing comma

A trailing comma, also known as a dangling comma, is a comma symbol that is typed after the last item of a list of elements. One of the major benefits when used with multilines, is that diff outputs are cleaner.

Array

You can use trailing comma in arrays :

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

Grouped use statement

Since PHP 7.2, you can use trailing comma in grouped use statement:

use Symfony\Component\HttpKernel\{
    Controller\ControllerResolverInterface,
    Exception\NotFoundHttpException,
    Event\PostResponseEvent,
};

Function and method call

Since PHP 7.3, you can use trailing comma when calling a function:

function myFunction($foo, $bar)
{
    return true;
}
$a = myFunction(
    'baz',
    'qux',
);

and when calling a method:

$f = new Foo();
$f->myMethod(
    'baz',
    'qux',
);

Function parameters

Since PHP 8.0, you can use trailing comma when declaring function parameters:

function myFunction(
    $foo,
    $bar,
)
{
    return true;
}

Closure's use statement

Since PHP 8.0, you can use trailing comma with closure's use statement:

function() use (
    $foo,
    $bar,
)
{
    return true;
}

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 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

Since PHP 8.0, 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;
}

Intersection type

Since PHP 8.1, you can use an "intersection type" (also known as "pure") that enforce that a given value belong to every types. For example this param needs to implement both Stringable and Countable interfaces:

function myFunction(Stringable&Countable $param): Stringable&Countable
{
    return $param;
}
Class Foo
{
    public function __toString() {
        return "something";
    }
}
myFunction(new Foo());
// TypeError: myFunction(): Argument #1 ($param) must be of type Stringable&Countable, Foo given

It also works with class property:

Class Foo
{
    public Stringable&Countable $bar;
}

Intersection type only supports class and interfaces. Scalar types (string, int, array, null, mixed, etc) are not allowed:

function myFunction(string&Countable $param)
{
    return $param;
}
// PHP Fatal error:  Type string cannot be part of an intersection type

External resource

Intersection types on PHP.Watch

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

or

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;

You can also swap variables with destructuring assignments, considering you have variable like:

$a = 'foo';
$b = 'bar';

So if you want to swap $a and $b instead of using a temporary variable like this:

$temp = $a;
$a = $b;
$b = $temp;

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

You can swap it using the list syntax:

list($a, $b) = [$b, $a];

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

Or since PHP 7.1, the shorthand syntax:

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

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

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, 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, 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 (~ august 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);
}

$a = countParameters('foo', null, [], true);
// $a = 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

Since PHP 8.0, it is possible to unpack an associative array (string-keyed) as it will use named arguments.

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, 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']

Associative array

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

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

You can unpack array with an already existing key:

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

You can unpack an empty array without error nor warning:

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

Named arguments

Since PHP 8.0, it is possible to pass in arguments by name instead of their position.

Considering a function like this:

function concat(string $first, string $second): string
{
    return $first . ' ' . $second;
}
$a = concat('foo', 'bar');
// $a = 'foo bar'

You can have the same result with the named argument syntax:

$a = concat(first: 'foo', second: 'bar');
// $a = 'foo bar'

You can call it with arguments in a different order:

$a = concat(second: 'bar', first: 'foo');
// $a = 'foo bar'

You can skip optional parameters:

function orGate(bool $option1 = false, bool $option2 = false, bool $option3 = false): bool
{
   return $option1 || $option2 || $option3;
}
$a = orGate(option3: true);
// $a = true

But you cannot skip a mandatory argument:

$a = concat(second: 'bar');
// TypeError: concat(): Argument #1 ($first) not passed

You cannot include some extra arguments:

$a = concat(first: 'foo', second: 'bar', third: 'baz');
// PHP Error:  Unknown named parameter $third

Named arguments also work with object constructor:

Class Foo
{
    public function __construct(
        public string $first,
        public string $second
    ) {}
    
}
$f = new Foo(first: 'bar', second: 'baz');

Named variadics

You can use named arguments with a variadic parameter:

function showParams(string ...$params): array
{
    return $params;
}
$a = showParams(first: 'foo', second: 'bar', third: 'baz');
// $a = ["first" => "foo", "second" => "bar", "third" => "baz"]

Unpacking named arguments

You can unpack an associative array as named arguments if keys 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

External resource

Short closures

Short closures, also called arrow functions, are an alternative way of writing anonymous functions in a shorter syntax. The main goal of short closures is to reduce verbosity when it is possible : if there is only a single expression.

Here is an example of a simple closure with only one expression :

$foo = function ($bar) {
    return $bar + 1;
}
$a = $foo(1);
// $a = 2

You can write the same function with a short closure :

$foo = fn ($bar) => $bar + 1;
$a = $foo(1);
// $a = 2

You cannot give a name to a short closure :

fn foo($bar) => $bar + 1;
// PHP Parse error: Syntax error, unexpected T_STRING, expecting '('

You can use short closure as function parameter. For example as a "callable" parameter in PHP's array_reduce:

$myArray = [10,20,30];

$total = array_reduce($myArray, fn ($carry, $item) => $carry + $item, 0);
// $total = 60

Type hinting is allowed as in a normal function :

fn (int $foo): int => $foo;

You don't need to use the return keyword as it is not allowed here :

fn ($foo) => return $foo;
// PHP Parse error: Syntax error, unexpected T_RETURN

Outer scope

The short closure doesn't require the use keyword to be able to access properties from the outer scope :

$bar = 10;
$baz = fn ($foo) => $foo + $bar;
$a = $baz(1);
//$a = 11

The keyword use is not allowed :

$bar = 10;
fn ($foo) use ($bar) => $foo + $bar;
// PHP Parse error: Syntax error, unexpected T_USE, expecting T_DOUBLE_ARROW

You could use $this as in any other function :

fn () => $this->foo + 1;

Match expression

Since PHP 8.0, there is a new match syntax similar to the switch syntax. As each matching case must only contain one expression, it can't be used and replace a switch statement in every situation. It is significantly shorter and easier to read though.

The match expression always returns a value. Each condition only allows a single expression, and it immediately returns the value and will not fall-through following conditions without an explicit break statement:

$foo = 'baz';
$a = match($foo) {
    'bar' => 1,
    'baz' => 2,
    'qux' => 3,
}
// $a = 2

It throws an exception when the value can't match:

$foo = 'qux';
$a = match($foo) {
    'bar' => 1,
    'baz' => 2,
}
// PHP Error:  Unhandled match value of type string

But it supports a default condition:

$foo = 'qux';
$a = match($foo) {
    'bar' => 1,
    'baz' => 2,
    default => 3,
}
// $a = 3

It allows multiple conditions in a single arm:

$foo = 'bar';
$a = match($foo) {
    'bar', 'baz' => 1,
    default => 2,
}
// $a = 1

It does strict type-safe comparison without type coercion (it's like using === instead of ==):

function showType($param) {
    return match ($param) {
        1 => 'Integer',
        '1' => 'String',
        true => 'Boolean',
    };
}

showType(1); // "Integer"
showType('1'); // "String"
showType(true); // "Boolean"

External resource

Match expression on PHP.Watch

Stringable interface

Since PHP 8.0, there is a new interface named Stringable, that indicates a class has a __toString() magic method. PHP automatically adds the Stringable interface to all classes that implement that method.

interface Stringable {
    public function __toString(): string;
}

When you define a parameter with Stringable type, it will check that the given class implements the Stringable interface:

class Foo {
    public function __toString(): string {
        return 'bar';
    }
}

function myFunction(Stringable $param): string {
    return (string) $param;
}
$a = myFunction(new Foo);
// $a = 'bar'

If a given class doesn't implement __toString(), you'll get an error:

class Foo {
}

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

A stringable type doesn't accept string:

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

Of course, to accept both string and Stringable, you can use a union type:

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

Enums

An Enum defines a new type, which has a fixed, limited number of possible legal values.

enum Status
{
    case DRAFT;
    case PUBLISHED;
    case ARCHIVED;
}

In an Enum, each case definition is case-sensitive. Historically, in PHP we generally represent "constants" with uppercase to distinguish them from normal variables, so it makes sense to stick to uppercase notation for enum cases. But note that this will work fine and define 3 different cases:

enum MyEnum
{
    case FOO;
    case foo;
    case Foo;
}

Now you can compare easily enums with type safe operator ===:

$statusA = Status::PENDING;

if ($statusA === Status::PENDING) {
    // true
}

Also an enum behaves like a traditional PHP object:

$statusA = Status::PENDING;
$statusB = Status::PENDING;
$statusC = Status::ARCHIVED;

$statusA === $statusB; // true
$statusA === $statusC; // false
$statusC instanceof Status; // true

You can use Enum to enforce types:

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

Enum methods

You can define methods with an Enum :

enum Status
{
    case DRAFT;
    case PUBLISHED;
    
    public function label(): string
    {
        return match($this) 
        {
            Status::DRAFT => 'Not ready...',   
            Status::PUBLISHED => 'Published !',   
        };
    }
}

then you can use methods on any enum instance:

$a = Status::DRAFT;
$a->label(); // 'Not ready...'

Backed values

Sometimes you need to assign a proper value to each enum case (ex: to store it in a database, comparison, etc). You should define the type of the back value. Here is an example with a backed value defined as an int :

enum HttpStatus: int
{
    case OK = 200;
    case NOT_FOUND = 404;
    case INTERNAL_SERVER_ERROR = 500;
}

And here is an example of a backed value defined as a string:

enum Status: string
{
    case DRAFT = 'draft';
    case PUBLISHED = 'published';
}

External resource

Multiple lines string syntax

When you want to define a string value that contains multiple lines, you generally use double quotes and escape line breaks:

$string = "Hello\nWorld";

Since PHP 7.3, there is a new option for specifying a string value over multiple lines. By placing it between an opening identifier and a closing identifier:

$string = <<<IDENTIFIER
Hello 
World
IDENTIFIER;

You can use any identifier you want, but it must be the same at the beginning and at the end of the string. It can't be a variable.

The closing identifier can be followed by other code on the same line:

$array = ['foo', 'bar', <<<IDENTIFIER
  hello
  world
  IDENTIFIER, 'baz', 'qux',
];

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Modern PHP Cheatsheet

Introduction

Motivation

Complementary Resources

Recent PHP releases

Table of Contents

Notions

Function default parameter value

Trailing comma

Array

Grouped use statement

Function and method call

Function parameters

Closure's use statement

Type declaration

Class property

Union type

Intersection type

External resource

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

Associative array

Named arguments

Named variadics

Unpacking named arguments

External resource

Short closures

Outer scope

Match expression

External resource

Stringable interface

Enums

Enum methods

Backed values

External resource

Multiple lines string syntax

External resource

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