comptime-if 0.1.1

Compile-time `if` procedural macro for Rust
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# comptime_if

[![docs.rs](https://img.shields.io/docsrs/comptime-if)](https://docs.rs/comptime-if)
[![crates.io](https://img.shields.io/crates/v/comptime-if.svg)](https://crates.io/crates/comptime-if)
[![License](https://img.shields.io/crates/l/comptime-if.svg)](https://crates.io/crates/comptime-if)

Simple compile-time conditional code inclusion for Rust macros.

This crate provides the `comptime_if!` macro, which allows you to include or exclude code blocks
based on compile-time boolean expressions.

This macro is useful for `macro_rules!` macros that accepts boolean parameters, like this:

```rust
mod test_module {
    use comptime_if::comptime_if;

    macro_rules! export {
        ($struct_name:ident, $($key:ident = $value:expr),* $(,)?) => {
            // `export = true` before `$(key = $value),*` works as the default value
            comptime_if! {
                if export where (export = true, $($key = $value),*) {
                    pub struct $struct_name;
                } else {
                    struct $struct_name;
                }
            }
        };
        // You might want to provide a default for the case when no key-value pairs are given
        ($struct_name:ident) => {
            export!($struct_name, );
        };
    }

    // Expands to `pub struct MyStruct;`
    export!(MyStruct, export = true);
}

// `MyStruct` is publicly accessible
use test_module::MyStruct;
```

# Syntax

The syntax for the `comptime_if!` macro is as follows:

```rust,ignore
comptime_if! {
    if (<condition>) where (<variable assignments>) {
        <code block if condition is true>
    } else {
        <code block if condition is false>
    }
}
```

- `<condition>`: A boolean expression that can include variables, logical operators and parentheses.
  You can omit the parentheses if the condition is a single variable or a negation of a single variable.
  Supported operators are:
  - `&&`, `&` (logical AND)
  - `||`, `|` (logical OR)
  - `^` (logical XOR)
  - `==` (logical EQUAL)
  - `!=` (logical NOT EQUAL)
  - `!` (logical NOT)
  - Parentheses `(` and `)` for grouping
- `<variable assignments>`: A comma-separated list of variable assignments in the form
  `<variable> = <boolean value>`. Multiple assignments to the same variable will use the last
  assignment.

# Example

```rust
use comptime_if::comptime_if;

comptime_if! {
    if condition where (condition = true) {
        println!("This code is included because condition is true.");
    } else {
        compile_error!("This code is excluded.");
    }
}

comptime_if! {
    if (a && (b || !c)) where (a = true, b = false, c = false) {
        println!("This code is included because the condition evaluates to true.");
    } else {
        compile_error!("This code is excluded.");
    }
}
```