Module compile_time 

Compile time utilities.

Compile Time Assertions

By default, dungeon_cell will generate compile time panics if an assertion made with this module fails. These panics will happen when rustc attempts to instantiate associated const values. This does not happen when running cargo check. They will only happen when actually fully building a project. This limitation is because generics can’t be used in normal const expressions (see the tracking issue for generic_const_exprs).

The resulting compiler errors don’t have any information on where the failing assert is located. The environment variable DUNGEON_CELL_RUNTIME_CHECKS can be enabled (it can have any value) while building dungeon_cell to have asserts made with this module generate runtime panics with a backtrace instead.

Example of enabling the environment variable using a .config/cargo.toml.

[env]
DUNGEON_CELL_RUNTIME_CHECKS = "true"

Example Assertion Failure

use dungeon_cell::compile_time::{SmallerOrEqualTo, UsizeAssert};
use dungeon_cell::Size;

SmallerOrEqualTo::<u16, Size<1>>::assert();

Output:

error[E0080]: evaluation of `<compile_time::SmallerOrEqualTo<u16, layout::Size<1>> as compile_time::UsizeAssert>::FAILED` failed
  --> src/compile_time.rs:40:26
   |
40 |     const FAILED: bool = do_usize_const_assert::<Self>(PanicMode::Monomorphized);
   |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at '

assertion failed: size of type T <= 1, type T has size = 2.

This error happens after monomorphization so the location of the code that caused
this to happen is not known. Add the `DUNGEON_CELL_RUNTIME_CHECKS` environment
variable when compiling to enable runtime panics with a backtrace.

', src/compile_time.rs:40:26

Structs

AlignmentSmallerOrEqualTo

SizeSmallerOrEqualTo

Assert size of T is smaller or equal to given size.

Enums

Comparison

Type of comparison.

Traits

UsizeAssert

Compile time evaluable assert for usize values.

Functions

const_transmute^⚠

Transmute for const contexts.

const_usize_assert

Const form of UsizeAssert::assert().