Crate vec_const

vec-const

This is a Rust crate that performs a bit of black-magic to allow vectors to be declared as const. Contains the macro: vec_const!. This macro is meant to mimic the vec! macro as closely as possible, but it does require a type to be specified (TBD: Is there a way around that?). See the below example:

pub struct AThing(u8, &'static str);

const A_VEC_CONST: ManuallyDrop<Vec<AThing>> = vec_const!(AThing, AThing(5, "wow"), AThing(2, "cool"));

fn main()
{
    assert_eq!(*TEST, vec!(AThing(5, "wow"), AThing(2, "cool")));
}

Disclaimer

Use at your own risk. This crate makes assumptions about various ABIs that are not guaranteed stable. Incorrect use can cause both heap corruption and access violations.

Danger Zone

This also comes with a vec_const_unsafe! macro that doesn’t wrap the vec in a ManuallyDrop. That means you have to be the one to make sure nothing is ever dropped when it shouldn’t be. This is hilariously unsafe and it doesn’t even have to decency to require unsafe blocks anywhere. You’re better off just leaving this one be.

Why?

I created this to solve a niche problem: I had a struct with a mostly trivial fields but also a Vec field. I had to share that struct among quite a few contexts using Rc<RefCell<Thing>>s, and was using RefCell::take to eventually acquire a modified version of that original Thing. Thing is, take replaces the RefCell content with whatever default returns; and allocating a ton of redundant Vecs was slowing things down. This was my solution to make that problem disappear. That said, while there are some cases this crate could genuinely be used for good, it’s most certainly an evil, rule-breaking crate. It laughs in the face of Rust’s safety-guarantees, and as such should never be used by anyone that hasn’t achieved ultimate enlightenment in the ways of all things memory-safety.

Macros

vec_const

Create a vector as a constant. Will return as a ManuallyDrop<Vec<T>>. Attempting to drop the inner vec will result in heap corruption, and attempting to mutate will result in an access violation. Clone if you need a mutable copy.

vec_const_unsafe

Like vec_const, but without the safety of the ManuallyDrop wrapper. Can easily cause catastrophic failure if misused.

Structs

VecFacade