I have const value, typed as struct. It contains config data for my App. This struct have const fn default function. Typical I define my const via struct update syntax (see down).
And I want to assert fields values of my struct. This is test example, which contains incorrect value my_const.b=1025:
#![feature(const_fn)]
pub struct MyStruct {
/// Values must be in [0..10]
pub a: u8,
/// Values must be in [0..1024]
pub b: u16,
}
impl MyStruct {
pub const fn default() -> Self {
Self { a: 10, b: 1024 } //This is correct values!
}
}
#[allow(non_upper_case_globals)]
pub const my_const: MyStruct = MyStruct {
b: 1025, //Incorrect!!!
..MyStruct::default()
};
//Static assert for my_const.a (1)
const CONDITION1: bool = my_const.a <= 10;
type __ASSERT1 = [i8; 0 - (!CONDITION1 as usize)];
const _tmp1: __ASSERT1 = [];
//Static assert for my_const.b (2)
const CONDITION2: bool = my_const.b <= 1024;
type __ASSERT2 = [i8; 0 - (!CONDITION2 as usize)];
const _tmp2: __ASSERT2 = [];
fn main() {}
And I got such compiler errors:
pc@home267:~/eclipse-workspace/tmp$ cargo build
Compiling tmp v0.1.0 (file:///home/pc/eclipse-workspace/tmp)
error[E0080]: constant evaluation error
--> src/main.rs:23:26
|
23 | const CONDITION1: bool = my_const.a <= 10;
| ^^^^^^^^^^ nonexistent struct field
|
note: for constant expression here
--> src/main.rs:25:1
|
25 | const _tmp1: __ASSERT1 = [];
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error[E0080]: constant evaluation error
--> src/main.rs:29:23
|
29 | type __ASSERT2 = [i8; 0 - (!CONDITION2 as usize)];
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ attempt to subtract with overflow
|
note: for constant expression here
--> src/main.rs:30:1
|
30 | const _tmp2: __ASSERT2 = [];
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: aborting due to 2 previous errors
If you want more information on this error, try using "rustc --explain E0080"
error: Could not compile `tmp`.
To learn more, run the command again with --verbose.
Assert No2 got error (my_const.b = 1025 not in [0..1024]), it is good.
But assert No1 must be compiled without errors (my_const.a = 10 in [0..10])! Instead of this I got strange error:
23 | const CONDITION1: bool = my_const.a < 10;
| ^^^^^^^^^^ nonexistent struct field
May be it is compiler bug?
Tools and environments:
- Rust compiler: rustc 1.26.0-nightly (3eeb5a665 2018-03-01)
- Target: any possible