try_from_fn in std::array - Rust (original) (raw)

Function try_from_fn

pub const fn try_from_fn<R, const N: usize, F>(
    cb: F,
) -> <<R as Try>::Residual as Residual<[<R as Try>::Output; N]>>::TryType

where
    R: Try,
    <R as Try>::Residual: Residual<[<R as Try>::Output; N]>,
    F: FnMut(usize) -> R,

🔬This is a nightly-only experimental API. (array_try_from_fn #89379)

Expand description

Creates an array [T; N] where each fallible array element T is returned by the cb call. Unlike from_fn, where the element creation can’t fail, this version will return an error if any element creation was unsuccessful.

The return type of this function depends on the return type of the closure. If you return Result<T, E> from the closure, you’ll get a Result<[T; N], E>. If you return Option<T> from the closure, you’ll get an Option<[T; N]>.

§Arguments

• cb: Callback where the passed argument is the current array index.

§Example

#![feature(array_try_from_fn)]

let array: Result<[u8; 5], _> = std::array::try_from_fn(|i| i.try_into());
assert_eq!(array, Ok([0, 1, 2, 3, 4]));

let array: Result<[i8; 200], _> = std::array::try_from_fn(|i| i.try_into());
assert!(array.is_err());

let array: Option<[_; 4]> = std::array::try_from_fn(|i| i.checked_add(100));
assert_eq!(array, Some([100, 101, 102, 103]));

let array: Option<[_; 4]> = std::array::try_from_fn(|i| i.checked_sub(100));
assert_eq!(array, None);