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//! Utilities for working with and combining the results of
//! [`Arbitrary::size_hint`][crate::Arbitrary::size_hint].
/// Protects against potential infinite recursion when calculating size hints
/// due to indirect type recursion.
///
/// When the depth is not too deep, calls `f` with `depth + 1` to calculate the
/// size hint.
///
/// Otherwise, returns the default size hint: `(0, None)`.
#[inline]
pub fn recursion_guard(
depth: usize,
f: impl FnOnce(usize) -> (usize, Option<usize>),
) -> (usize, Option<usize>) {
const MAX_DEPTH: usize = 20;
if depth > MAX_DEPTH {
(0, None)
} else {
f(depth + 1)
}
}
/// Take the sum of the `lhs` and `rhs` size hints.
#[inline]
pub fn and(lhs: (usize, Option<usize>), rhs: (usize, Option<usize>)) -> (usize, Option<usize>) {
let lower = lhs.0 + rhs.0;
let upper = lhs.1.and_then(|lhs| rhs.1.map(|rhs| lhs + rhs));
(lower, upper)
}
/// Take the sum of all of the given size hints.
///
/// If `hints` is empty, returns `(0, Some(0))`, aka the size of consuming
/// nothing.
#[inline]
pub fn and_all(hints: &[(usize, Option<usize>)]) -> (usize, Option<usize>) {
hints.iter().copied().fold((0, Some(0)), and)
}
/// Take the minimum of the lower bounds and maximum of the upper bounds in the
/// `lhs` and `rhs` size hints.
#[inline]
pub fn or(lhs: (usize, Option<usize>), rhs: (usize, Option<usize>)) -> (usize, Option<usize>) {
let lower = std::cmp::min(lhs.0, rhs.0);
let upper = lhs
.1
.and_then(|lhs| rhs.1.map(|rhs| std::cmp::max(lhs, rhs)));
(lower, upper)
}
/// Take the maximum of the `lhs` and `rhs` size hints.
///
/// If `hints` is empty, returns `(0, Some(0))`, aka the size of consuming
/// nothing.
#[inline]
pub fn or_all(hints: &[(usize, Option<usize>)]) -> (usize, Option<usize>) {
if let Some(head) = hints.first().copied() {
hints[1..].iter().copied().fold(head, or)
} else {
(0, Some(0))
}
}
#[cfg(test)]
mod tests {
#[test]
fn and() {
assert_eq!((5, Some(5)), super::and((2, Some(2)), (3, Some(3))));
assert_eq!((5, None), super::and((2, Some(2)), (3, None)));
assert_eq!((5, None), super::and((2, None), (3, Some(3))));
assert_eq!((5, None), super::and((2, None), (3, None)));
}
#[test]
fn or() {
assert_eq!((2, Some(3)), super::or((2, Some(2)), (3, Some(3))));
assert_eq!((2, None), super::or((2, Some(2)), (3, None)));
assert_eq!((2, None), super::or((2, None), (3, Some(3))));
assert_eq!((2, None), super::or((2, None), (3, None)));
}
#[test]
fn and_all() {
assert_eq!((0, Some(0)), super::and_all(&[]));
assert_eq!(
(7, Some(7)),
super::and_all(&[(1, Some(1)), (2, Some(2)), (4, Some(4))])
);
assert_eq!(
(7, None),
super::and_all(&[(1, Some(1)), (2, Some(2)), (4, None)])
);
assert_eq!(
(7, None),
super::and_all(&[(1, Some(1)), (2, None), (4, Some(4))])
);
assert_eq!(
(7, None),
super::and_all(&[(1, None), (2, Some(2)), (4, Some(4))])
);
}
#[test]
fn or_all() {
assert_eq!((0, Some(0)), super::or_all(&[]));
assert_eq!(
(1, Some(4)),
super::or_all(&[(1, Some(1)), (2, Some(2)), (4, Some(4))])
);
assert_eq!(
(1, None),
super::or_all(&[(1, Some(1)), (2, Some(2)), (4, None)])
);
assert_eq!(
(1, None),
super::or_all(&[(1, Some(1)), (2, None), (4, Some(4))])
);
assert_eq!(
(1, None),
super::or_all(&[(1, None), (2, Some(2)), (4, Some(4))])
);
}
}