Rust.md

Table of Contents

• Rust
  • Undefined behaviors
    • Floating point to integer casts
  • Memory error
    • Pattern guard consuming value being matched

Rust

Undefined behaviors

Floating point to integer casts

fn main() {
    let a = 360.0f32;
    println!("{:?}", a as u8);
    
    let a = 360.0f32 as u8;
    println!("{:?}", a);
    
    println!("{:?}", 360.0f32 as u8);
}

Expected result: 3x the same (despite the u8 overflow)

Results:

104  // this is consistent between runs
208  // this varies on every single run!
255  // this is consistent between runs

Tested with:

• rustc 1.33.0
• rustc 1.35.0-nightly

See also: rust-lang/rust#10184

Memory error

---

Pattern guard consuming value being matched

fn main() {
    let a = Some("...".to_owned());
    let b = match a {
        Some(_) if { drop(a); false } => None,
        x                             => x,
    };
    println!("{:?}", b);
}

Expected result: build error (matched value a is dropped in pattern guard)

Result: builds fine, and prints random values or crashes

Reason:

Tested with:

• rustc 1.18.0 (03fc9d622 2017-06-06)
• rustc 1.20.0-nightly (859c3236e 2017-06-26)

See also: rust-lang/rust#31287

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