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impls_index_meta

Procedural macro implementation for function indexing in impl blocks.

Overview

impls_index_meta is the proc-macro companion crate for impls_index. It provides macros that wrap each function in an impl block under a named macro, enabling function discovery and indexing at compile time.

Important: This crate should not be used directly. Use the impls_index crate which re-exports this functionality.

Scope

Responsibility

impls_index_meta is responsible for providing procedural macros that generate wrapper macros for functions in impl blocks, enabling compile-time function indexing.

In-Scope

  • impls! macro: Wrap impl block functions under named macros
  • impls1!, impls2!, impls3! macros: Variants for different contexts
  • Function analysis: Parse function signatures
  • Macro generation: Generate wrapper macros for each function

Out-of-Scope

  • Runtime behavior: Pure compile-time code generation
  • User-facing API: Use impls_index crate instead
  • Function body modification: Only wraps, doesn't transform

Boundaries

  • Upstream: Uses macro_tools for syntax parsing
  • Downstream: Re-exported by impls_index crate
  • Compile-time only: No runtime dependencies

Architecture

Module Structure

impls_index_meta/
├── src/
│   └── lib.rs              # Proc-macro entry point
├── Cargo.toml
├── readme.md
└── spec.md

Macro Expansion

// Input
impls!
{
  fn add( a: i32, b: i32 ) -> i32 { a + b }
  fn sub( a: i32, b: i32 ) -> i32 { a - b }
}

// Generates (conceptual):
macro_rules! add { ... }
macro_rules! sub { ... }
fn add( a: i32, b: i32 ) -> i32 { a + b }
fn sub( a: i32, b: i32 ) -> i32 { a - b }

Public API

Macros

impls!

Index functions in impl block.

use impls_index::impls;

impls!
{
  fn greet( name: &str ) -> String
  {
    format!( "Hello, {}!", name )
  }
}

// Function is available both directly and via generated macro
let msg = greet( "World" );

Feature Flags

Feature Default Description
enabled ✓ Enable the crate
full - All features

Dependencies and Consumers

Dependencies

Dependency Purpose
macro_tools Syntax parsing utilities

Consumers

  • impls_index - Re-exports this crate's macros

Design Rationale

Why Function Indexing?

Function indexing enables:

  1. Compile-time function discovery
  2. Macro-based function invocation
  3. Metaprogramming over function sets

Related Crates

Crate Relationship
impls_index Parent facade crate
macro_tools Upstream syntax utilities