Macro std::compile_fail

macro compile_fail($reason, $args/* ... */) { ... }

source

Causes the compilation to fail if reached.

This is useful when conditional compilation is used with #[cfg(...)] attributes, but it can also be used in generic context (e.g. with when expressions).

Can accept format arguments, which are formatted using the same syntax as std::fmt::format_args!. For obvious reasons, they must be const-evaluable.

Examples

fn fork() -> bool {
    #[cfg(target_os="windows")]
    compile_fail!("fork() is not supported on Windows");

    libc::fork() == 0
}

let is_child = fork();
if is_child {
    println!("Hello from child");
} else {
    println!("Hello from parent");
}
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fn type_of_value<T>(v: T) -> &[u8] {
    when v is i32 {
        "i32"
    } else when v is &[u8] {
        "&[u8]"
    } else {
        compile_fail!("unsupported type")
    }
}

println!("{}", type_of_value(1)); // "i32"
println!("{}", type_of_value("hello world")); // "&[u8]"
// println!("{}", type_of_value(true)); // Would fail to compile
Run this example