op_result

Syntactic sugar for writing associated type algebra with operator expressions.

Provides two macros:

• output!: Expands operator expressions to associated type outputs
• #[op_result]: Transforms operator expressions in where clauses into trait bounds. Supports two syntaxes: (): IsDefined<{ ... }> and [(); ...]:

Example

use op_result::op_result;
use op_result::output;

#[op_result]
fn add<T, U>(a: T, b: U) -> output!(T + U)
where
    [(); T + U]:,
{
    a + b
}

let result = add(1, 2);
assert_eq!(result, 3);

Usage

output! macro

Transforms output!(T + U) into <T as core::ops::Add<U>>::Output. Works recursively for nested expressions, preserving parentheses for operator precedence.

use op_result::op_result;
use op_result::output;

#[op_result]
fn add<T, U>(a: T, b: U) -> output!(T + U)
where
    [(); T + U]:,
{
    a + b
}

let result = add(1, 2);

#[op_result] attribute macro

Transforms operator expressions in where clauses into trait bounds.

use op_result::op_result;
use op_result::output;

#[op_result]
fn example_sub<T, U>(a: T, b: U) -> output!(T - U - U)
where
    [(); T - U - U]:,
    U: Copy,
{
    (a - b) - b
}

The output type can be assigned using the = operator:

use op_result::op_result;

#[op_result]
fn example_output_assignment<T, U, V>(a: T, b: U) -> V
where
    [(); T + U = V]:,
{
    a + b
}

Both [(); ...]: and (): IsDefined<{ ... }> syntaxes are supported.

Syntax Controls

You can control which syntaxes are processed using attribute parameters:

• #[op_result] - Default: both syntaxes enabled, uses IsDefined as the marker trait name
• #[op_result(any_syntax)] - Explicitly enable both syntaxes
• #[op_result(any_syntax, TraitName)] - Enable both syntaxes with a custom marker trait name
• #[op_result(marker_trait_syntax)] - Only process (): IsDefined<{ ... }> syntax
• #[op_result(marker_trait_syntax, TraitName)] - Only process marker trait syntax with a custom trait name
• #[op_result(well_formedness_syntax)] - Only process [(); ...]: syntax

The optional second parameter (trait name) defaults to IsDefined and is only valid with marker_trait_syntax or any_syntax.

Supported Operators

All binary and unary operators from core::ops that have an associated Output type:

• + → [core::ops::Add]
• - → [core::ops::Sub]
• * → [core::ops::Mul]
• / → [core::ops::Div]
• % → [core::ops::Rem]
• & → [core::ops::BitAnd]
• | → [core::ops::BitOr]
• ^ → [core::ops::BitXor]
• << → [core::ops::Shl]
• >> → [core::ops::Shr]
• ! → [core::ops::Not] (unary operator)
• - → [core::ops::Neg] (unary operator)

License

Licensed under either of Apache License, Version 2.0 or MIT license at your option.