Type declarations
Type declarations can be added to function arguments, return values, and, as of PHP 7.4.0, class properties. They ensure that the value is of the specified type at call time, otherwise a TypeError is thrown.
Note:
When overriding a parent method, the child's method must match any return type declaration on the parent. If the parent doesn't define a return type, then the child method may do so.
Single types
| Type | Description | Version |
|---|---|---|
| Class/interface name |
The value must be an instanceof the given class or interface.
|
|
| self |
The value must be an instanceof the same class as the one
in which the type declaration is used.
Can only be used in classes.
|
|
| parent |
The value must be an instanceof the parent of the class
in which the type declaration is used.
Can only be used in classes.
|
|
| array | The value must be an array. | |
| callable | The value must be a valid callable. Cannot be used as a class property type declaration. | |
| bool | The value must be a boolean value. | |
| float | The value must be a floating point number. | |
| int | The value must be an integer. | |
| string | The value must be a string. | |
| iterable |
The value must be either an array or an instanceof Traversable.
|
PHP 7.1.0 |
| object | The value must be an object. | PHP 7.2.0 |
| mixed | The value can be any value. | PHP 8.0.0 |
Aliases for the above scalar types are not supported.
Instead, they are treated as class or interface names.
For example, using boolean as a type declaration
will require the value to be an instanceof the class or interface
boolean, rather than of type bool:
<?php
function test(boolean $param) {}
test(true);
?>
Output of the above example in PHP 8:
Warning: "boolean" will be interpreted as a class name. Did you mean "bool"? Write "\boolean" to suppress this warning in /in/9YrUX on line 2 Fatal error: Uncaught TypeError: test(): Argument #1 ($param) must be of type boolean, bool given, called in - on line 3 and defined in -:2 Stack trace: #0 -(3): test(true) #1 thrown in - on line 2
mixed
mixed is equivalent to the union type object|resource|array|string|int|float|bool|null. Available as of PHP 8.0.0.
Examples
Example #1 Basic class type declaration
<?php
class C {}
class D extends C {}
// This doesn't extend C.
class E {}
function f(C $c) {
echo get_class($c)."\n";
}
f(new C);
f(new D);
f(new E);
?>
Output of the above example in PHP 8:
C D Fatal error: Uncaught TypeError: f(): Argument #1 ($c) must be of type C, E given, called in /in/gLonb on line 14 and defined in /in/gLonb:8 Stack trace: #0 -(14): f(Object(E)) #1 thrown in - on line 8
Example #2 Basic interface type declaration
<?php
interface I { public function f(); }
class C implements I { public function f() {} }
// This doesn't implement I.
class E {}
function f(I $i) {
echo get_class($i)."\n";
}
f(new C);
f(new E);
?>
Output of the above example in PHP 8:
C Fatal error: Uncaught TypeError: f(): Argument #1 ($i) must be of type I, E given, called in - on line 13 and defined in -:8 Stack trace: #0 -(13): f(Object(E)) #1 thrown in - on line 8
Example #3 Basic return type declaration
<?php
function sum($a, $b): float {
return $a + $b;
}
// Note that a float will be returned.
var_dump(sum(1, 2));
?>
The above example will output:
float(3)
Example #4 Returning an object
<?php
class C {}
function getC(): C {
return new C;
}
var_dump(getC());
?>
The above example will output:
object(C)#1 (0) {
}
Nullable type
As of PHP 7.1.0, type declarations can be marked nullable by prefixing the
type name with a question mark (?).
This signifies that the value can be of the specified type or null.
Example #5 Nullable argument type declaration
<?php
class C {}
function f(?C $c) {
var_dump($c);
}
f(new C);
f(null);
?>
The above example will output:
object(C)#1 (0) {
}
NULL
Example #6 Nullable return type declaration
<?php
function get_item(): ?string {
if (isset($_GET['item'])) {
return $_GET['item'];
} else {
return null;
}
}
?>
Note:
It is possible to achieve nullable arguments by making
nullthe default value. This is not recommended as this breaks during inheritance.Example #7 Old way to make arguments nullable
<?php
class C {}
function f(C $c = null) {
var_dump($c);
}
f(new C);
f(null);
?>The above example will output:
object(C)#1 (0) { } NULL
Composite types
It is possible to combine simple types into composite types. PHP allows types to be combined in the following ways:
- Union of simple types. As of PHP 8.0.0.
- Intersection of class-types (interfaces and class names). As of PHP 8.1.0.
It is not possible to combine intersection types with union types.
Union types
A union type declaration accepts values of multiple different simple types,
rather than a single one.
Union types are specified using the syntax T1|T2|....
Union types are available as of PHP 8.0.0.
Nullable union types
The null type is supported as part of unions,
such that T1|T2|null can be used to create a nullable union.
The existing ?T notation is considered a shorthand
for the common case of T|null.
null cannot be used as a standalone type.
false pseudo-type
The false literal type is supported as part of unions,
and is included as for historical reasons many internal functions return
false instead of null for failures.
A classic example of such a function is strpos().
false cannot be used as a standalone type (including
nullable standalone type).
As such, false, false|null
and ?false are not permitted.
The true literal type does not
exist.
Intersection types
An intersection type declaration accepts values which satisfies multiple
class-type declarations, rather than a single one.
Intersection types are specified using the syntax T1&T2&....
Intersection types are available as of PHP 8.1.0.
Duplicate and redundant types
To catch simple bugs in composite type declarations, redundant types that can be detected without performing class loading will result in a compile-time error. This includes:
-
Each name-resolved type may only occur once. Types such as
int|string|INTorCountable&Traversable&COUNTABLEresult in an error. - Using mixed results in an error.
-
For union types:
- If bool is used, false cannot be used additionally.
- If object is used, class types cannot be used additionally.
- If iterable is used, array and Traversable cannot be used additionally.
-
For intersection types:
- Using a type which is not a class-type results in an error.
- Using either self, parent, or static results in an error.
Note: This does not guarantee that the type is “minimal”, because doing so would require loading all used class types.
For example, if A and B are class
aliases, then A|B remains a legal union type, even
though it could be reduced to either A or
B.
Similarly, if class B extends A {}, then A|B
is also a legal union type, even though it could be reduced to just
A.
<?php
function foo(): int|INT {} // Disallowed
function foo(): bool|false {} // Disallowed
function foo(): int&Traversable {} // Disallowed
function foo(): self&Traversable {} // Disallowed
use A as B;
function foo(): A|B {} // Disallowed ("use" is part of name resolution)
function foo(): A&B {} // Disallowed ("use" is part of name resolution)
class_alias('X', 'Y');
function foo(): X|Y {} // Allowed (redundancy is only known at runtime)
function foo(): X&Y {} // Allowed (redundancy is only known at runtime)
?>
Return only types
void
void is a return type indicating the function does not
return a value.
Therefore it cannot be part of a union type declaration.
Available as of PHP 7.1.0.
Note:
Returning by reference from a void function is deprecated as of PHP 8.1.0, because such a function is contradictory. Previously, it already emitted the following
E_NOTICEwhen called:Only variable references should be returned by reference.<?php
function &test(): void {}
?>
never
never is a return type indicating the function does not
return. This means that it either calls exit(), throws
an exception, or is an infinite loop.
Therefore it cannot be part of a union type declaration.
Available as of PHP 8.1.0.
never is, in type theory parlance, the bottom type. Meaning it is the subtype of every other type and can replace any other return type during inheritance.
static
The value must be an instanceof the same class as the one the
method is called in.
Available as of PHP 8.0.0.
Strict typing
By default, PHP will coerce values of the wrong type into the expected scalar type declaration if possible. For example, a function that is given an int for a parameter that expects a string will get a variable of type string.
It is possible to enable strict mode on a per-file basis. In strict mode, only a value corresponding exactly to the type declaration will be accepted, otherwise a TypeError will be thrown. The only exception to this rule is that an int value will pass a float type declaration.
Function calls from within internal functions will not be affected by
the strict_types declaration.
To enable strict mode, the declare statement is used with the
strict_types declaration:
Note:
Strict typing applies to function calls made from within the file with strict typing enabled, not to the functions declared within that file. If a file without strict typing enabled makes a call to a function that was defined in a file with strict typing, the caller's preference (coercive typing) will be respected, and the value will be coerced.
Note:
Strict typing is only defined for scalar type declarations.
Example #8 Strict typing for arguments values
<?php
declare(strict_types=1);
function sum(int $a, int $b) {
return $a + $b;
}
var_dump(sum(1, 2));
var_dump(sum(1.5, 2.5));
?>
Output of the above example in PHP 8:
int(3) Fatal error: Uncaught TypeError: sum(): Argument #1 ($a) must be of type int, float given, called in - on line 9 and defined in -:4 Stack trace: #0 -(9): sum(1.5, 2.5) #1 thrown in - on line 4
Example #9 Coercive typing for argument values
<?php
function sum(int $a, int $b) {
return $a + $b;
}
var_dump(sum(1, 2));
// These will be coerced to integers: note the output below!
var_dump(sum(1.5, 2.5));
?>
The above example will output:
int(3) int(3)
Example #10 Strict typing for return values
<?php
declare(strict_types=1);
function sum($a, $b): int {
return $a + $b;
}
var_dump(sum(1, 2));
var_dump(sum(1, 2.5));
?>
The above example will output:
int(3) Fatal error: Uncaught TypeError: sum(): Return value must be of type int, float returned in -:5 Stack trace: #0 -(9): sum(1, 2.5) #1 thrown in - on line 5
Coercive typing with union types
When strict_types is not enabled, scalar type declarations
are subject to limited implicit type coercions.
If the exact type of the value is not part of the union, then the target type
is chosen in the following order of preference:
- int
- float
- string
- bool
As an exception, if the value is a string and both int and float are part
of the union, the preferred type is determined by the existing
“numeric string” semantics.
For example, for "42" int is chosen,
while for "42.0" float is chosen.
Note:
Types that are not part of the above preference list are not eligible targets for implicit coercion. In particular no implicit coercions to the
nullandfalsetypes occur.
Example #11 Example of types being coerced into a type part of the union
<?php
// int|string
42 --> 42 // exact type
"42" --> "42" // exact type
new ObjectWithToString --> "Result of __toString()"
// object never compatible with int, fall back to string
42.0 --> 42 // float compatible with int
42.1 --> 42 // float compatible with int
1e100 --> "1.0E+100" // float too large for int type, fall back to string
INF --> "INF" // float too large for int type, fall back to string
true --> 1 // bool compatible with int
[] --> TypeError // array not compatible with int or string
// int|float|bool
"45" --> 45 // int numeric string
"45.0" --> 45.0 // float numeric string
"45X" --> true // not numeric string, fall back to bool
"" --> false // not numeric string, fall back to bool
"X" --> true // not numeric string, fall back to bool
[] --> TypeError // array not compatible with int, float or bool
?>
Misc
Example #12 Typed pass-by-reference Parameters
Declared types of reference parameters are checked on function entry, but not when the function returns, so after the function had returned, the argument's type may have changed.
<?php
function array_baz(array &$param)
{
$param = 1;
}
$var = [];
array_baz($var);
var_dump($var);
array_baz($var);
?>
Output of the above example in PHP 8:
int(1) Fatal error: Uncaught TypeError: array_baz(): Argument #1 ($param) must be of type array, int given, called in - on line 9 and defined in -:2 Stack trace: #0 -(9): array_baz(1) #1 thrown in - on line 2
Example #13 Catching TypeError
<?php
declare(strict_types=1);
function sum(int $a, int $b) {
return $a + $b;
}
try {
var_dump(sum(1, 2));
var_dump(sum(1.5, 2.5));
} catch (TypeError $e) {
echo 'Error: ', $e->getMessage();
}
?>
Output of the above example in PHP 8:
int(3) Error: sum(): Argument #1 ($a) must be of type int, float given, called in - on line 10
