front-vec

Efficiently-prependable Vec and String types.

Exposes two types: FrontVec<T> and FrontString. Each implements a push_front method which efficiently prepends a value onto the front of the data structure.

The types implement Deref so that they can be used like slices/&strs.

Unstable Warning

This crate uses the following unstable features, and therefore requires the nightly compiler.

#![feature(ptr_internals, maybe_uninit_slice)]

unsafe Warning

This is an "in-development" crate. I'm not certain all uses of unsafe are valid yet. Please don't use this for anything important yet.

Potential Use Cases

Efficient Cons-Lists

My use-case is for packing data together in memory more eficiently than a cons-list, but with the same API as one.

Representation in Memory

my_front_vec =
[len: usize     = 3]
[cap: usize     = 8]
[buf: Unique<T> = *]
                  |
                  |
                  v
[?, ?, ?, ?, ?, x1, x2, x3]

This diagram shows the memory representation of a FrontVec<T> which corresponds to the the Vec vec![x1, x2, x3]. The question marks (?) represent uninitialized data.

Downsides

This representation (I believe) does not allow the use of the realloc function, which assumes memory at the front of the buffer is initialized. So a Front{Vec,String} is slightly less efficient because of that.

Disclaimer

This is my first time writing unsafe code, so any safety audit contributions are certainly welcome!