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 (Php8.0 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:
Table of Contents
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 hint
With Type hinting you can specify the expected data type for a property. 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
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 hint
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 $bar;
}
Nullable type hint
When a parameter has no type, it can accept null value:
function myFunction($param) {
return $param;
}
$a = myFunction(null);
// $a = null
But as soon as a parameter has a type hint, 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 hint, 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 hint 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 {} // PHP Fatal error: Void type cannot be nullable
// or
function myFunction() : void|null {} // 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'
// $c = 'baz'
Or the shorthand syntax:
[$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()
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"
// $c = 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 $param) { ... }
// PHP Fatal error: Only the last parameter can be variadic
You can have only one variadic parameter:
function countParameters(string ...$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
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']
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