Rust: What is the difference between transmute and cast?

transmute — reinterpret bits. cast — conversion.

transmute:

• Same size required.
• Bit reinterpretation.
• Very unsafe.

cast:

• Type conversion.
• May change size.
• Less unsafe.

1let x: f32 = 3.14;
2let y: i32 = unsafe { std::mem::transmute(x) };  // Bit reinterpret
3
4let x: f32 = 3.14;
5let y: i32 = x as i32;  // Truncation

Key: transmute for bit reinterpretation, cast for conversion.