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Mojo reference

This section includes the Mojo API references:

How to read the Mojo API docs​

Mojo syntax is covered in detail in the Mojo manual. Here's a quick cheat-sheet on reading struct and function signatures.

Arguments​

Function arguments appear in parentheses after the function name:

def example_fn(pos: Int, /, pos_or_kw: Int, *, kw_only: Bool = False):
    ...

Here's a quick overview of some special syntax in the argument list:

You may also see argument names prefixed with one or two stars (*):

def myfunc2(*names, **attributes) raises:

An argument may also be preceded by an argument convention, which indicates how the value is passed:

def sort(mut names: List[String]):

The most common conventions are:

  • read(default): the callee receives an immutable reference to the value.
  • mut: the callee receives a mutable reference to the value.
  • owned: the callee receives ownership of a value.

For details and a complete list of argument conventions, see Argument conventions.

Parameters​

Mojo structs and functions can take parameters. Parameters are evaluated at compilation time, and act as constants at runtime. Parameter lists are enclosed in square brackets:

struct ExampleStruct[size: Int, //, thing: Thing[size]]:

Parameters that occur before a double-slash (//) in the parameter list are infer-only parameters. You usually don't need to specify infer-only parameters; as the name suggests, they're usually inferred.

Like arguments, parameters can be positional-only, keyword-or-positional, or keyword-only, and they can be required or optional. The /, *, and = characters have the same meaning in parameter lists as they do in argument lists.

Standard library​

The Mojo standard library provides nearly everything you'll need for writing Mojo programs, including basic data types like Int and SIMD, collection types like List, reusable algorithms and modules to support GPU programming.

Top-level packages:

MAX AI kernels library​

The MAX AI kernels library provides a collection of highly optimized, reusable compute kernels for high-performance numerical and AI workloads. These kernels serve as the foundational building blocks for writing MAX custom operations or standalone GPU kernels that are portable across CPUs and GPUs.

Top-level packages:

Decorators​

A Mojo decorator is a higher-order function that modifies or extends the behavior of a struct, a function, or some other code.

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