numeric-casts

name	numeric-casts
description	Rules for numeric type conversions in Luma. Use when writing or reviewing code that casts between integer or float types, especially across different widths.

Numeric Casts in Luma

Widening casts (smaller → larger)

Always use From/Into, never as:

// Correct
let x: u64 = u64::from(byte);
let x: u64 = byte.into();

// Wrong — triggers clippy::cast_lossless
let x = byte as u64;

clippy::cast_lossless enforces this automatically.

Narrowing casts (larger → smaller)

Only use as when the bound is provably safe and documented:

// Acceptable — bound is clear from context
let idx = offset as usize; // offset is always < usize::MAX by construction

// Preferred when bound is not obvious
let idx = usize::try_from(offset).expect("offset fits usize");

If overflow is possible and silent truncation is wrong, use try_from and handle the error explicitly.