Why does Deque.at return T instead of ?T

Explain
1

I understand that the implementation for zig 0.16.0 is

pub fn at(deque: *const Self, index: usize) T {
    assert(index < deque.len);
    return deque.buffer[deque.bufferIndex(index)];
}

I would have expected to be something like this.

pub fn at(deque: *const Self, index: usize) ?T {
    if(index >= deque.len) return null
    return deque.buffer[deque.bufferIndex(index)];
}

Is there a reason why the function does not return an optional? the optional would be better because it gives you the static check instead of a runtime crash.

Since this is my first question about the source code, i thought id ask first before i suggest changes.

2

My guess is that since the caller already has access to the deque’s length, they figure it’s up to the caller to bounds-check the index and simply assert that the caller did.
This enables cases where, for better performance, when the caller knows for certain that they don’t need to bounds-check and the index will be in bounds, the function can just blindly trust the index the caller provided.

3

i’d agree, except that the caller would also have access to the buffer directly and would not need to access items via access functions. I wonder if it’s just a temporary implementation on purpose

1 Like
4

Looks like it was done for performance improvement

Assert below is kind of guard

assert(index < deque.len);

btw i also think that ?T is better…