macro_rules! assertc_eq {
($left:expr, $right:expr $(, $($fmt:tt)* )? ) => { ... };
}
Expand description
For asserting that two values are equal.
This macro is only evaluated at compile-time if used in a context that requires it (eg: in the expression assigned to a const _: () =
)
§Formatting
This uses the same syntax for formatting arguments as const_panic::concat_panic
.
By default, this only supports primitive types as arguments, to format arrays or custom types you must enable const_panic
’s "non_basic"
feature.
To pass user-defined types, they must implement both of these traits as described in their docs:
§Examples
§Zipping slices
This example requires the "iter"
feature
use konst::{iter, slice};
const A: &[u8] = &[3, 5, 8, 13];
const B: &[u8] = &[0, 1, 2, 3];
const C: &[(u8, u8)] = &{
konst::assertc_eq!(A.len(), B.len());
iter::collect_const!((u8, u8) =>
slice::iter_copied(A),
zip(slice::iter_copied(B)),
)
};
assert_eq!(C, [(3, 0), (5, 1), (8, 2), (13, 3)]);
If either slice was a different length, this would be the compile-time error:
error[E0080]: evaluation of constant value failed
--> src/macros/assert_macros.rs:79:5
|
10 | konst::assertc_eq!(A.len(), B.len());
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at '
assertion failed: LEFT == RIGHT
left: `3`
right: `4`
', src/macros/assert_macros.rs:10:5
§User-defined type
This example demonstrates formatting of user-defined types.
The const_panic::PanicFmt
derive that this example uses
requres enabling const_panic
’s "derive"
feature.
use konst::assertc_eq;
use konst::const_panic::PanicFmt;
const _: () = assert_same_layout(layout_for!(u32), layout_for!(i32));
#[track_caller]
const fn assert_same_layout(left: Layout, right: Layout) {
assertc_eq!{left, right, "layout mismatch"}
}
#[derive(PanicFmt)]
struct Layout {
type_name: &'static str,
size: usize,
alignment: usize,
}
konst::impl_cmp!{
impl Layout;
pub const fn const_eq(&self, other: &Self) -> bool {
konst::const_eq!(self.size, other.size) &&
konst::const_eq!(self.alignment, other.alignment)
}
}
impl Layout {
pub const fn new<T>(type_name: &'static str) -> Self {
Self {
type_name,
size: std::mem::size_of::<T>(),
alignment: std::mem::align_of::<T>(),
}
}
}
macro_rules! layout_for {
($ty:ty) => {
Layout::new::<$ty>(stringify!($ty))
}
} use layout_for;
If the types were changed, the example would fail compilation with this error:
error[E0080]: evaluation of constant value failed
--> src/macros/assert_macros.rs:120:15
|
6 | const _: () = assert_same_layout(layout_for!(u32), layout_for!([u8; 4]));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at '
assertion failed: LEFT == RIGHT
left: `Layout { type_name: "u32", size: 4, alignment: 4 }`
right: `Layout { type_name: "[u8; 4]", size: 4, alignment: 1 }`
: layout mismatch', src/macros/assert_macros.rs:6:15