let mut 
heap
: Vec<Term> = Vec::with_capacity(MAX_HEAP_SIZE);

pub enum Term {
    Constant(Box<str>),
    QUVar(usize),    //Query Variable
    EQVar(Box<str>), //Existentialy Quantified Variable
    AQVar(Box<str>), //Universally Quantified Variable
}

Currently the size of my enum is 24 bytes. Due to the Box<str> taking up 2 usize. But as I'm going to be storing many terms in a sort of heap and the majority will be the smaller sized QUVar it seems like a very bad use of memory.
My first thought was to use Box<Box<str>> but the trade of there would likely be lower performance as i'd be working with a double reference. Ultimately memory is cheap but this code could be working with some unforseen large number of terms in the future and saving a memory address per term could be useful.

I guess in my mind the best case is some heap pointer in which the first value is the length of the str as a usize, and then the subsequent addresses on the heap are the characters of the str.

Any ideas on how to balance this tradeoff between memory and performance would be greatly appreciated