I tried this code:

use std::hint::black_box;

pub fn demo(data: &[u8]) {
    assert!(!data.is_empty());

    let mut chunks = data.chunks_exact(1024);

    let last_block = if chunks.remainder().is_empty() {
        chunks.next_back().expect("this is impossible")
    } else {
        chunks.remainder()
    };

    black_box(last_block);
}

When compiled with optimizations enabled and viewing the assembly code, I expected to not see a reference to the string "this is impossible". Since there's an assert that the input data is non-empty, then either there will be a remainder, there will be at least one chunk, or both.

Instead, the assembly contains a reference to the expect string and there's a conditional call to expect_failed.

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• 1.81.0-nightly (2024-07-12 c6727fc)