Rust: Don't unnecessarily create new Vecs for every request.

[dcormier]

Using .unwrap_or(&Vec::new()) will allocate create a new Vec every time the code is executed, whether or not the value being unwrapped is None.

Using .unwrap_or_default() will only allocate create a new Vec if the value being unwrapped is None.

[CosmicHorrorDev]

Vec::new() actually does not allocate. I would be surprised if this caused a perf diff. Quoting the docs

The vector will not allocate until elements are pushed onto it.

[dcormier]

A new Vec struct is allocated and returned by Vec::new() (source). It's internal storage is empty, though.

I have not run a benchmark comparison.

[CosmicHorrorDev]

I think we're using terminology differently. I'm used to allocate meaning specifically heap allocations, not just creating some struct in general

[coder543]

I have to agree that calling Vec::new() shouldn't really affect performance since it doesn't cause heap allocations.