Macro const_format::assertc

macro_rules! assertc {
    ($($parameters:tt)*) => { ... };
}

Available on crate feature assertc only.

Compile-time assertions with formatting.

This macro requires the “assertcp” feature to be exported.

Syntax

This macro uses the same syntax for the format string and formatting arguments as the formatc macro.

Limitations

This macro has these limitations:

• It can only use constants that involve concrete types, so while a Type::<u8>::FOO in an argument would be fine, Type::<T>::FOO would not be (T being a type parameter).

• Integer arguments must have a type inferrable from context, as described in the integer arguments section in the root module .

Examples

Passing assertion

#![feature(const_mut_refs)]

use const_format::assertc;

use std::mem::size_of;

assertc!(
    size_of::<&str>() == size_of::<&[u8]>(),
    "The size of `&str`({} bytes) and `&[u8]`({} bytes) aren't the same?!?!",
    size_of::<&str>(),
    size_of::<&[u8]>(),
);

Failing assertion

This example demonstrates a failing assertion, and how the compiler error looks like as of 2021-09-18.

#![feature(const_mut_refs)]

use const_format::assertc;

const L: u64 = 2;
const R: u64 = 2;

assertc!(L + R == 5, "{} plus {} isn't 5, buddy", L,  R);

This is the compiler output:

error[E0080]: evaluation of constant value failed
  --> src/macros/assertions.rs:132:10
   |
12 | assertc!(L + R == 5, "{} plus {} isn't 5, buddy", L,  R);
   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at '
assertion failed.
2 plus 2 isn't 5, buddy
', src/macros/assertions.rs:12:10