Ace the Rust Interview

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intermediate · order 80

The usize underflow trap

arr-usize-01Related book chapters: 15 (optional — this page is complete on its own)usizeunderflow

Slug: arr-usize-01 · Paired reading: Chapter 15

Prompt

fn prev_index(i: usize) -> Option<usize> — return i - 1 when i > 0, else None. Never write bare i - 1 in debug (underflow panic) or wrap in release. Use checked_sub / i.checked_sub(1).