Mojo decorators

A Mojo decorator modifies or extends the behavior of a struct, function, or other declaration at compile time. You place the decorator on the line above the declaration it applies to, prefixed with @.

@fieldwise_init
struct Point:
    var x: Float64
    var y: Float64

After the @, a decorator is followed by a name, with optional arguments in parentheses. Each decorator goes on its own line. You can stack multiple decorators on a single declaration:

@fieldwise_init
@align(64)
struct CacheLine:
    var data: SIMD[DType.float32, 16]

Decorators apply bottom-up: the one closest to the declaration is applied first.

No custom decorators

Mojo doesn't support custom decorators. The decorators in this section are built into the compiler.

Decorators

The following pages describe each built-in decorator with examples.

📄️ @align

Specifies a minimum alignment for a struct.

📄️ @always_inline

Copies the body of a function directly into the body of the calling function.

📄️ @compiler.register

Registers a custom operation for use with the MAX Graph API.

📄️ @__copy_capture

Captures register-passable typed values by copy.

📄️ @deprecated

Mojo's `@deprecated` decorator marks outdated APIs and schedules them for removal. When used with the `use` parameter, it also provides migration suggestions.

📄️ @doc_hidden

Hides declarations from generated documentation.

📄️ @explicit_destroy

Prevents automatic destruction by a `__del__()` method and requires explicit cleanup through named destructor methods.

📄️ @export

Marks a function for export.

📄️ @fieldwise_init

Generates fieldwise constructor for a struct.

📄️ @implicit

Marks a constructor as eligible for implicit conversion.

📄️ @no_inline

Prevents a function from being inlined.

📄️ @parameter

Executes a function or if statement at compile time.

📄️ @staticmethod

Declares a struct method as static.

Decorator targets

Not every decorator works on every declaration. This table shows which decorators are valid on which targets.

Decorator	struct	def	method	trait	comptime	var	field
@align	yes
@always_inline		yes	yes
@compiler.register	yes
@__copy_capture			yes
@deprecated	yes	yes	yes	yes	yes
@doc_hidden	yes	yes	yes		yes		yes
@explicit_destroy	yes
@export		yes
@fieldwise_init	yes
@implicit			yes
@no_inline		yes	yes
@nonmaterializable	yes
@parameter			yes
@staticmethod			yes