Macro expansion
Macro expansion is the compile-time transformation of a macro invocation into source tokens or language constructs according to its definition and expansion rules.
Modern C, Third Edition
Macro expansion is the recursive process of replacing a macro invocation and any expandable macros in its arguments with source tokens.
- How it is used
- Defines how function-like macro invocations become source tokens during preprocessing.
- How deep it goes
- Explains argument parsing, recursive substitution, rescanning, recursion prevention, and early translation-phase timing.
- Examples
- Uses BYTECOPY expansion, nested STRINGIFY and STRGY definitions, __LINE__, and trace output.
- What you can do after
- Evaluate macro invocations by tracing argument expansion, parameter substitution, rescanning, and stringification order.
Idiomatic Rust
A macro expansion is the compiler-generated source or language construct produced from a macro invocation.
- How it is used
- Explains how declarative macros accept token trees, repeat arguments, and generate calls to other macros.
- How deep it goes
- Demonstrates matching, repetition, nesting, and compiler tracing, then stops at the built-in implementation of format_args!.
- Examples
- Uses special_println!, var_print!, formatted output, and trace_macros! expansion output.
- What you can do after
- Evaluate macro behavior by reading repeated token patterns and tracing nested expansions into generated Rust constructs.
Write Powerful Rust Macros
Macro expansion is the process of replacing a macro invocation with the source code generated or transformed by that macro.
- How it is used
- Explains how Rust turns macro invocations into ordinary code before checking, compilation, and execution.
- How deep it goes
- Traces matcher selection, transcriber insertion, preserved punctuation, and expansion inspection, while stopping short of procedural-macro internals.
- Examples
- Uses my_vec!() expanding to Vec::new(), derive-generated implementations, and cargo expand output for debugging.
- What you can do after
- Diagnose macro-generated code with cargo expand, including invalid output and errors originating in generated functions.
Read how Write Powerful Rust Macros explains macro expansion →
Clojure: The Essential Reference
Macro expansion is the compile-time transformation of a macro invocation into the expression that will be evaluated.
- How it is used
- Supports REPL exploration, macro writing, debugging, and some code-analysis tooling.
- How deep it goes
- Explains one-step, repeated outer, and recursive expansion, stopping short of evaluating or fully analyzing generated code.
- Examples
- Uses when-first and and forms to compare expansion depth and expose short-circuit implementation.
- What you can do after
- Diagnose macro behavior by inspecting returned forms and compare expansion depth with named Clojure functions.
Read how Clojure: The Essential Reference explains macro expansion →
Related concepts
- macroproduced by · A macro is a named construct that expands or transforms source code, commands, or templates before or during execution.
- cargo-expandused by · cargo-expand is a Cargo subcommand that displays the source code generated by expanding Rust macros.
- logical AND operatorimplemented by · A logical AND operator is a Boolean conjunction that produces true exactly when all operands have true truth values.
- macro invocationproduced by · A macro invocation is source syntax that requests expansion of a macro, typically with an associated name and arguments.
- replacement textuses · Replacement text is the sequence of preprocessing tokens specified by a macro definition for insertion when the macro expands.
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