Code shared from the Rust Playground

playground.rs

trait HeapSize {
    fn heap_size(&self) -> usize;
}


pub struct KnownElementHeapSize<T>(pub T);

trait KnownHeapSize {
    const S: usize;
}

impl KnownHeapSize for u8 {
    const S: usize = 0;
}

impl <E: KnownHeapSize> HeapSize for KnownElementHeapSize<Vec<E>> {
    fn heap_size(&self) -> usize {
        self.0.capacity() * std::mem::size_of::<E>() + self.0.len() * E::S
    }
}


fn main() {
    println!("Hello, world!");
}