Generic Types

Edit pageLast modified: 02 February 2025

Each type can take arguments containing other type declarations. Validation of arguments and their number lies on the implementing side; the parser does not limit their number or nesting and does not check their semantic correctness in any way.

Each argument is enclosed in triangle brackets < and > and separated by a comma (,).

note

Please note that throughout the documentation the term " template argument " is used because the similar term " template parameter " is used to describe a declaration.

If the PHP language supported generic types, then the declaration (in pseudo-language) of the type:

  • interface Traversable<node of array-key, TValue of mixed> would contain parameters

and the reference to the type:

  • Traversable<int<0, max>, string> would contain arguments.

tip

Reference to an existing class, interface or enum with template arguments.

Path\To\ExampleClass<T, U>

tip

Reference to builtin type with template arguments containing other generics.

iterable<int<0, max>, Collection<User>>

tip

Trailing comma is allowed.

HashMap<Request, User,>

Call-Site Hints

Each template argument allows you to define an additional hint, which can be used, for example, in static analyzers to indicate the call-site variance.

warning

One template argument can contain only one hint.

tip

Any identifier (in this case " covariant ") before the template argument`s type is acceptable.

HashMap<array-key, covariant Request>

List Syntax

In addition to modern list declarations such as list<int> or array<array-key, int>, the legacy int[] syntax is allowed.

tip

List (array) of User objects.

User[]

tip

List of list (nested array) of User objects.

User[][]

Attributes

Each template argument allows you to define list of additional attributes. An attribute is additional metadata for an argument.

tip

Simple attribute with one argument for each template argument.

HashMap<#[name("key")] T, #[name("value")] U>

tip

Multiple attributes in one group.

HashMap<#[name("key"), out] T>

tip

Multiple attribute groups.

HashMap<#[name("key")] #[out] T>