type casting

[TanvirSiddik]

I tried this code:

pub fn type_casting() {
    let something: u8 = 255;
    let something_i8 = something as i8;
    println!("{}", something_i8);
    println!("{}", something);
}

I expected to see this happen: i was expecting somekind of error, not even runtime error

Instead, this happened: *i get
-1
255
as output this may cause bugs in application
*

Meta

rustc --version --verbose:

<version>

rustc 1.85.0 (4d91de4 2025-02-17)
binary: rustc
commit-hash: 4d91de4
commit-date: 2025-02-17
host: x86_64-pc-windows-msvc
release: 1.85.0
LLVM version: 19.1.7

Backtrace

<backtrace>

[jieyouxu]

See:

• Tracking Issue for integer_sign_cast #125882
• and its stabilization PR Stabilize (and const-stabilize) integer_sign_cast #137026 for the more explicit uN::cast_signed version of this.
• Reference for as cast: https://doc.rust-lang.org/reference/expressions/operator-expr.html#type-cast-expressions.

I'm going to close this as inactionable because while it's known that as casts are a confusing mix of a bunch of behaviors, it's likely too noisy to warn on existing code, and more explicit methods are being added to address such use cases to make it unambiguous.