Macro iter_comprehensions::product

macro_rules! product {
    ($t:ty : $e:expr; $($rest:tt)*) => { ... };
    ($t:ty : $($rest:tt)*) => { ... };
    ($e:expr; $($rest:tt)*) => { ... };
    ($($rest:tt)*) => { ... };
}

A product expression.

The two possible macro calls

product!(EXPR; i1 in RANGE1, COND2, ..., ik in RANGEk)
product!(i1 in RANGE1, COND2, ..., ik in RANGEk, EXPR)

are roughly equivalent to

map!(EXPR; i1 in RANGE1, COND2, ..., ik in RANGEk).product()
map!(i1 in RANGE1, COND2, ..., ik in RANGEk, EXPR).product()

Example

The following expression corresponds to the mathematical expression $\prod_{i=1}^5 i$.

use iter_comprehensions::product;
assert_eq!(product!(i in 1..=5, i), 120);
assert_eq!(product!(i; i in 1..=5), 120);

It is also possible to specify the return type of the product in case it cannot be infered automatically.

use iter_comprehensions::product;
assert_eq!(product!(usize : i; i in 1..=5), 120);