Rust panics if index out of bounds

[alexispurslane]

fn main () {
    let x = vec![1, 2, 3];
    println!("Got: {}", x[88]);
}

This code compiles just fine, but, when I run it, I get an ICE, or something similar:

thread '<main>' panicked at 'index out of bounds: the len is 3 but the index is 88', ../src/libcollections/vec.rs:1047

Note that this is the same problem as in #28217. Here are the lines it references:

#[stable(feature = "rust1", since = "1.0.0")]
impl<T> Index<usize> for Vec<T> {
    type Output = T;

    #[inline]
    fn index(&self, index: usize) -> &T {
        // NB built-in indexing via `&[T]`
        &(**self)[index]
    }
}

I'm not sure if this is intended behavior or not, but it seems odd.

[jdm]

This is intended behaviour - the [x] form of indexing panics, because it cannot return a reference to an element that doesn't exist. .get(x) returns an Option<T>, so it doesn't panic. The panicking behaviour is documented at https://doc.rust-lang.org/nightly/reference.html#index-expressions .

[shamiao]

recent url of index expressions document:
(stable) https://doc.rust-lang.org/reference.html#index-expressions
(nightly) https://doc.rust-lang.org/nightly/reference/expressions.html#index-expressions