Macro assertcp_eq

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

Compile-time equality assertion with formatting.

For examples look here

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 formatcp macro.

Limitations

This macro can only take constants of these types as arguments:

• &str

• i*/u* (all the primitive integer types).

• char

• bool

This macro also 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

use const_format::assertcp_eq;

const NAME: &str = "Bob";

assertcp_eq!(NAME, "Bob", "Guessed wrong, the right value is {}", NAME);

const SUM: u8 = 1 + 2 + 3;
assertcp_eq!(6u8, SUM, "Guessed wrong, the right value is {}", SUM);

Failing assertion

This example demonstrates a failing assertion, and how the compiler error looks like as of 2023-10-14.

use const_format::assertcp_eq;

use std::mem::size_of;

#[repr(C)]
struct Type(u16, u16, u16);

assertcp_eq!(size_of::<Type>(), size_of::<[u16; 2]>(), "Whoops, `Type` is too large");

This is the compiler output:

error[E0080]: evaluation of constant value failed
  --> const_format/src/macros/assertions/assertcp_macros.rs:235:14
   |
12 | assertcp_eq!(size_of::<Type>(), size_of::<[u16; 2]>(), "Whoops, `Type` is too large");
   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at '
assertion failed: `(left == right)`
 left: `6`
right: `4`
Whoops, `Type` is too large
', const_format/src/macros/assertions/assertcp_macros.rs:12:14