`ref_patterns` shouldn't be triggered when sub slices are involved

[c410-f3r]

The use of ref actually prevents a compilation error in the following scenario.

#![deny(clippy::ref_patterns)]

fn foo(bar: &[u8]) -> u8 {
    if let &[a, b, ref _rest @ .., c, d, e] = bar {
        a + b + c + d + e
    } else {
        0
    }
}

Of course, [a, b, _rest @ .., c, d, e] = bar is still possible but it is cumbersome to defer all those bytes.

#![deny(clippy::ref_patterns)]

fn foo(bar: &[u8]) -> u8 {
    if let [a, b, _rest @ .., c, d, e] = bar {
        *a + *b + *c + *d + *e
    } else {
        0
    }
}

In my particular use-case I deal with +30 individual bytes, which makes things even more cumbersome.

[profetia]

Using &bar will result in valid code and you do not neeed * everywhere:

fn foo(bar: &[u8]) -> u8 {
    if let [a, b, _rest @ .., c, d, e] = &bar {
        a + b + c + d + e
    } else {
        0
    }
}

[c410-f3r]

Compiles because the standard library implements Add for references. De-referencing is still necessary to get owned values.