compose-idents 0.0.2

Rust macro that makes possible to concatenate idents from multiple parts.
Documentation

Build Crates.io Version docs.rs

compose-idents

A procedural macro that allows to construct identifiers from one or more arbitrary parts.

Motivation

Rust's declarative macros do not allow generating new identifiers, because they are designed to operate on the syntactic level (as opposed to the lexical level) using simple pattern matching.

For example the following code won't work:

macro_rules! my_macro {
    ($name:ident) => {
        my_$name_fn() -> u32 {
            42
        }
    };
}

my_macro!(foo);

This is why there is a need for a macro that allows to construct new identifiers.

Usage

Here is how the macro works:

use compose_idents::compose_idents;


compose_idents!(my_fn_1 = [foo, _, "baz"]; my_fn_2 = [spam, _, eggs]; {
    fn my_fn_1() -> u32 {
        123
    }

    fn my_fn_2() -> u32 {
        321
    }
});


assert_eq!(foo_baz(), 123);
assert_eq!(spam_eggs(), 321);

Here is a more practical example for how to auto-generate names for macro-generated tests for different data types:

use std::ops::Add;
use compose_idents::compose_idents;

fn add<T: Add<Output = T>>(x: T, y: T) -> T {
  x + y
}

macro_rules! generate_add_tests {
    ($($type:ty),*) => {
      $(
        compose_idents!(test_fn = [test_add_, $type]; {
          fn test_fn() {
            let actual = add(2 as $type, 2 as $type);
            let expected = (2 + 2) as $type;

            assert_eq!(actual, expected);
          }
        });
      )*
    };
}

generate_add_tests!(u8, u32, u64);

test_add_u8();
test_add_u32();
test_add_u64();

For more usage examples look into examples/ and tests/ directories of the repository.

Alternatives

There some other projects dedicated to identifier manipulation:

Development

The following standards are followed to maintain the project: