A while let pattern attempts to match the pattern, and enters the body if the
match was successful. If the match is irrefutable (when it cannot fail to
match), use a regular let-binding inside a loop instead. For instance:
struct Irrefutable(i32);
let irr = Irrefutable(0);
// This fails to compile because the match is irrefutable.
while let Irrefutable(x) = irr {
// ...
}Try this instead:
struct Irrefutable(i32);
let irr = Irrefutable(0);
loop {
let Irrefutable(x) = irr;
// ...
}