If we want a constant context, we can say so. Because Rust is expression oriented we can write for example a loop (though if you're unfamiliar with Rust it may not be clear why a for loop can't work yet, other loops are fine) and wrap the whole expression in a const block and that'll be evaluated at compile time. For example:
let a = const {
let mut x: u64 = 0;
let mut k = 5;
loop {
if k == 0 {
break x;
}
k -= 1;
x += 2;
x *= x;
}
};
Yeah, it's nice that const blocks are stable now. Before them, you had to use hacks like defining a trait impl with an associated const, which was verbose and messy.
(If I recall correctly, one of the big questions was "Will const blocks unreachable at runtime still be evaluated at compile time?" It looks like the answer was to leave it unspecified.)
