From b23a0473b366134ffa792fc52f538c0577a3a397 Mon Sep 17 00:00:00 2001 From: Tim Vermeulen Date: Tue, 12 Mar 2019 17:52:26 +0100 Subject: [PATCH] Remove the projection part of select_fold1 --- src/libcore/iter/traits/iterator.rs | 77 ++++++++--------------------- 1 file changed, 21 insertions(+), 56 deletions(-) diff --git a/src/libcore/iter/traits/iterator.rs b/src/libcore/iter/traits/iterator.rs index 861e9c3157a7..199c6cdfa48b 100644 --- a/src/libcore/iter/traits/iterator.rs +++ b/src/libcore/iter/traits/iterator.rs @@ -2008,12 +2008,8 @@ pub trait Iterator { #[stable(feature = "rust1", since = "1.0.0")] fn max(self) -> Option where Self: Sized, Self::Item: Ord { - select_fold1(self, - |_| (), - // switch to y even if it is only equal, to preserve - // stability. - |_, x, _, y| *x <= *y) - .map(|(_, x)| x) + // switch to y even if it is only equal, to preserve stability. + select_fold1(self, |x, y| x <= y) } /// Returns the minimum element of an iterator. @@ -2038,12 +2034,8 @@ pub trait Iterator { #[stable(feature = "rust1", since = "1.0.0")] fn min(self) -> Option where Self: Sized, Self::Item: Ord { - select_fold1(self, - |_| (), - // only switch to y if it is strictly smaller, to - // preserve stability. - |_, x, _, y| *x > *y) - .map(|(_, x)| x) + // only switch to y if it is strictly smaller, to preserve stability. + select_fold1(self, |x, y| x > y) } /// Returns the element that gives the maximum value from the @@ -2062,15 +2054,11 @@ pub trait Iterator { /// ``` #[inline] #[stable(feature = "iter_cmp_by_key", since = "1.6.0")] - fn max_by_key(self, f: F) -> Option + fn max_by_key(self, mut f: F) -> Option where Self: Sized, F: FnMut(&Self::Item) -> B, { - select_fold1(self, - f, - // switch to y even if it is only equal, to preserve - // stability. - |x_p, _, y_p, _| x_p <= y_p) - .map(|(_, x)| x) + // switch to y even if it is only equal, to preserve stability. + select_fold1(self.map(|x| (f(&x), x)), |(x_p, _), (y_p, _)| x_p <= y_p).map(|(_, x)| x) } /// Returns the element that gives the maximum value with respect to the @@ -2092,12 +2080,8 @@ pub trait Iterator { fn max_by(self, mut compare: F) -> Option where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering, { - select_fold1(self, - |_| (), - // switch to y even if it is only equal, to preserve - // stability. - |_, x, _, y| Ordering::Greater != compare(x, y)) - .map(|(_, x)| x) + // switch to y even if it is only equal, to preserve stability. + select_fold1(self, |x, y| compare(x, y) != Ordering::Greater) } /// Returns the element that gives the minimum value from the @@ -2115,15 +2099,11 @@ pub trait Iterator { /// assert_eq!(*a.iter().min_by_key(|x| x.abs()).unwrap(), 0); /// ``` #[stable(feature = "iter_cmp_by_key", since = "1.6.0")] - fn min_by_key(self, f: F) -> Option + fn min_by_key(self, mut f: F) -> Option where Self: Sized, F: FnMut(&Self::Item) -> B, { - select_fold1(self, - f, - // only switch to y if it is strictly smaller, to - // preserve stability. - |x_p, _, y_p, _| x_p > y_p) - .map(|(_, x)| x) + // only switch to y if it is strictly smaller, to preserve stability. + select_fold1(self.map(|x| (f(&x), x)), |(x_p, _), (y_p, _)| x_p > y_p).map(|(_, x)| x) } /// Returns the element that gives the minimum value with respect to the @@ -2145,12 +2125,8 @@ pub trait Iterator { fn min_by(self, mut compare: F) -> Option where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering, { - select_fold1(self, - |_| (), - // switch to y even if it is strictly smaller, to - // preserve stability. - |_, x, _, y| Ordering::Greater == compare(x, y)) - .map(|(_, x)| x) + // switch to y even if it is strictly smaller, to preserve stability. + select_fold1(self, |x, y| compare(x, y) == Ordering::Greater) } @@ -2693,34 +2669,23 @@ pub trait Iterator { } } -/// Select an element from an iterator based on the given "projection" -/// and "comparison" function. +/// Select an element from an iterator based on the given "comparison" +/// function. /// /// This is an idiosyncratic helper to try to factor out the /// commonalities of {max,min}{,_by}. In particular, this avoids /// having to implement optimizations several times. #[inline] -fn select_fold1(mut it: I, - mut f_proj: FProj, - mut f_cmp: FCmp) -> Option<(B, I::Item)> - where I: Iterator, - FProj: FnMut(&I::Item) -> B, - FCmp: FnMut(&B, &I::Item, &B, &I::Item) -> bool +fn select_fold1(mut it: I, mut f: F) -> Option + where + I: Iterator, + F: FnMut(&I::Item, &I::Item) -> bool, { // start with the first element as our selection. This avoids // having to use `Option`s inside the loop, translating to a // sizeable performance gain (6x in one case). it.next().map(|first| { - let first_p = f_proj(&first); - - it.fold((first_p, first), |(sel_p, sel), x| { - let x_p = f_proj(&x); - if f_cmp(&sel_p, &sel, &x_p, &x) { - (x_p, x) - } else { - (sel_p, sel) - } - }) + it.fold(first, |sel, x| if f(&sel, &x) { x } else { sel }) }) }