Const Generics

const generics let you parameterize types and functions with compile‑time constant values, enabling generic code over sizes, indices, or other fixed values.

rust

impl<T, const N: u64> AbiEncode for [T; N] where T: AbiEncode {
    fn abi_encode(self, buffer: Buffer) -> Buffer {
        let mut buffer = buffer;
        let mut i = 0;
        while i < N {
            buffer = self[i].abi_encode(buffer);
            i += 1;
        };
        buffer
    }
}

This allowed us to implement all the std traits for arrays, string arrays etc.

AbiEncode
AbiDecode
Clone
Debug
Hash
Iterator
PartialEq
Eq
etc.

"const generics" can be used on structs, enums, functions, impls etc.

rust

struct S<T, const N: u64> {}

impl<const Z: u64> OneVariant<Z> {
    pub fn return_n(self) -> u64 {
        Z
    }
}

enum OneVariant<const N: u64> {
    A: [u64; N],
}

fn const_with_const_generics<const B: u64>() {
    const A: u64 = B + 1;
    let _ = __dbg(A);
}

and can be used like any other constant.

rust

impl<T, const N: u64> AbiDecode for [T; N] {
    ...
    fn abi_decode(ref mut buffer: BufferReader) -> [T; N] {
        const LENGTH: u64 = __size_of::<T>() * N;
        let mut array = [0u8; LENGTH];
        ...
    }
}