For a function like this:
fn generate_even(a: i32, b: i32) -> impl Iterator<Item = i32> {
(a..b).filter(|x| x % 2 == 0)
}
I want to make it generic, instead of the concrete type i32
I want to have any type that is range-able and provide a filter implementation.
Tried the formula below without success:
fn generate_even(a: T, b: T) -> impl Iterator<Item = T>
where T: // range + filter + what to put here?
{
(a..b).filter(|x| x % 2 == 0)
}
How can something like this be implemented?
use std::ops::Range;
use std::ops::Rem;
use std::cmp::PartialEq;
fn generate_even<T>(a: T, b: T) -> impl Iterator<Item = T>
where
Range<T>: Iterator<Item = T>,
T: Copy + Rem<Output = T> + From<u8> + PartialEq
{
let zero: T = 0_u8.into();
let two: T = 2_u8.into();
(a..b).filter(move |&x| x % two == zero)
}
fn main() {
let even_u8s = generate_even(0_u8, 11_u8);
let even_i16s = generate_even(0_i16, 11_i16);
let even_u16s = generate_even(0_u16, 11_u16);
// and so on
let even_u128s = generate_even(0_u128, 11_u128);
}
The hardest part of the solution is implementing x % 2 == 0
in a generic way because by default Rust interprets integer literals as i32
s but you want your function to be generic across all possible integer types, which means you have to produce a 2
and 0
value of whatever integer type the caller specifies, and the simplest way to do that is to bound T
by From<u8>
which allows us to transform any value from 0
to 256
into any integer type (with i8
being the only exception). The above solution is generic and works for all integer types except i8
.