Macros
The functionality and syntax of Rust can be extended with custom definitions
called macros. They are given names, and invoked through a consistent
syntax: some_extension!(...)
.
There are two ways to define new macros:
- Macros by Example define new syntax in a higher-level, declarative way.
- Procedural Macros define function-like macros, custom derives, and custom attributes using functions that operate on input tokens.
Macro Invocation
Syntax
MacroInvocation :
SimplePath!
DelimTokenTreeDelimTokenTree :
(
TokenTree*)
|[
TokenTree*]
|{
TokenTree*}
TokenTree :
Tokenexcept delimiters | DelimTokenTreeMacroInvocationSemi :
SimplePath!
(
TokenTree*)
;
| SimplePath!
[
TokenTree*]
;
| SimplePath!
{
TokenTree*}
A macro invocation expands a macro at compile time and replaces the invocation with the result of the macro. Macros may be invoked in the following situations:
- Expressions and statements
- Patterns
- Types
- Items including associated items
macro_rules
transcribers- External blocks
When used as an item or a statement, the MacroInvocationSemi form is used
where a semicolon is required at the end when not using curly braces.
Visibility qualifiers are never allowed before a macro invocation or
macro_rules
definition.