attr

Declares an attribute macro: attr name(FnDecl f, …) -> Code { … }.

It runs at compile time on the item marked #[name(…)] (a function, method, class or enum) and its output replaces that item. The first parameter is a FnDecl or TypeDecl; the others bind the attribute’s arguments. A module cannot use its own macros: import them from a provider module.

use macro::{FnDecl, Code, raw};

/// Keeps the function and adds a `name_twice` wrapper.
attr twice(FnDecl f) -> Code {
    return quote items {
        ${raw(f.source)}
        fn ${raw(f.name.str())}_twice() -> int {
            return ${raw(f.name.str())}() * 2;
        }
    };
}

See also#

• fn: Declares a function, a method, or (written in an expression) an anonymous function.
• let: Declares a mutable local variable.
• const: Declares a binding that cannot be reassigned: a local, a module constant, or a class field that is set only by new.
• static: Declares a module-level or class-level slot shared by the whole program, or a method without self.
• readonly: A read-only view of a value: nothing reachable through it can be changed.
• if: Runs a block when a bool condition is true.
• else: Introduces the branch of an if that runs when its condition is false (or its pattern does not match).
• while: Repeats a block while a bool condition is true.