Lib.rs

› No standard library
#unreachable

no-std inconceivable

inconceivable! is a macro which closely parallels std::unreachable, or std::panic. The primary difference is that when this crate is configured with the ub_inconceivable option it will emit the core::hint::unreachable_unchecked to hint for the compiler to understand a condition should never occur. Generally compiler(s) (the LLVM) assume UB won’t happen. This macro offers the “best of both worlds”, it provides a solid way of asserting/testing behavior in local builds, but also a way of stripping branches out of final release builds. Please Note: This crate is created purely to inject undefined behavior into stable, safe rust. Systematic usage is unwise, and not recommended.

by Cody Laeder

1 unstable release

Uses old Rust 2015

0.9.0 Jan 31, 2020

#413 in No standard library

MIT license

9KB
93 lines

feature_macros

This crate allows for controling how safe/unsafe other crates are.

Example

This macro can (but should not necessarily) be used identically to unreachable! or panic!.


    match x {
        Foo::Bar => bar(&x),
        Foo::Baz => baz(&x),
        _ => inconceivable!(),
    }

Developer Controllable Options

  • ub_inconceivable: This controls the semantics of the inconceivable! macro. When this options is not supplied (or when this options is supplied, and the crate is compiled with rustc --version < 1.27) inconceivable! will simply alias unreachable!. When this option is supplied (and the crate is compiled with rustc --version >= 1.27) this will instead emit unreachable_uncheck() which is UB.

Developer Uncontrollable Options

  • RUSTC_VERSION_GE_1_27: States if rustc --version >= 1.27 this is used as a feature check.

No runtime deps

~20KB