Avoid any intermediate heap allocations when advancing indexes

mdznr · Kyle Macomber · mdznr · commit 4c4100f83d4d · 2021-01-11T14:59:37.000-08:00
Co-authored-by: Kyle Macomber &lt;kmacomber@apple.com&gt;
diff --git a/Sources/Algorithms/Combinations.swift b/Sources/Algorithms/Combinations.swift
@@ -124,7 +124,8 @@ extension Combinations: Sequence {
         if kRange.lowerBound < kRange.upperBound {
           let advancedLowerBound = kRange.lowerBound + 1
           kRange = advancedLowerBound..<kRange.upperBound
-          self.indexes = Array(base.indices.prefix(kRange.lowerBound))
+          indexes.removeAll(keepingCapacity: true)
+          indexes.append(contentsOf: base.indices.prefix(kRange.lowerBound))
         }
       }
       

Original file line number	Diff line number	Diff line change
`@@ -124,7 +124,8 @@ extension Combinations: Sequence {`
`124`	`124`	`if kRange.lowerBound < kRange.upperBound {`
`125`	`125`	`let advancedLowerBound = kRange.lowerBound + 1`
`126`	`126`	`kRange = advancedLowerBound..<kRange.upperBound`
`127`		`- self.indexes = Array(base.indices.prefix(kRange.lowerBound))`
	`127`	`+ indexes.removeAll(keepingCapacity: true)`
	`128`	`+ indexes.append(contentsOf: base.indices.prefix(kRange.lowerBound))`
`128`	`129`	`}`
`129`	`130`	`}`
`130`	`131`