> https://github.com/apple/swift/blob/master/stdlib/public/core/CollectionAlgorithms.swift.gyb
> https://github.com/apple/swift/blob/master/stdlib/public/core/Sort.swift.gyb

可以清楚地看到,使用introsort进行排序
最大递归深度为2 * floor(log(N)),并切换到
插入排序小于20个元素的范围.

旧答案：定义可比较的结构并在断点中设置&lt ;:

struct MyStruct : Comparable {
    let val : Int
}

func ==(x: MyStruct,y: MyStruct) -> Bool {
    println("\(x.val) ==  \(y.val)")
    return x.val == y.val
}
func <(x: MyStruct,y: MyStruct) -> Bool {
    println("\(x.val) < \(y.val)")
    return x.val < y.val // <--- SET BREAKPOINT HERE
}

var array = [MyStruct]()
for _ in 1 ... 30 {
    array.append(MyStruct(val: Int(arc4random_uniform(1000))))
}
sort(&array)

显示以下堆栈回溯：

(lldb) bt
* thread #1: tid = 0x5a00,0x00000001001cb806 sort`sort. Swift.Bool + 454 at main.swift:22,queue = 'com.apple.main-thread',stop reason = breakpoint 1.1
  * frame #0: 0x00000001001cb806 sort`sort. Swift.Bool + 454 at main.swift:22
    frame #1: 0x00000001001cb62b sort`protocol witness for Swift._Comparable.(Swift._Comparable.Self.Type)(Swift._Comparable.Self,Swift._Comparable.Self) -> Swift.Bool in conformance sort.MyStruct : Swift._Comparable + 27 at main.swift:20
    frame #2: 0x00000001000f5a98 sort`Swift._partition (inout A,Swift.Range) -> A.Index + 3224
    frame #3: 0x00000001000f756a sort`Swift._introSortImpl (inout A,Swift.Range,Swift.Int) -> () + 2138
    frame #4: 0x00000001000f6c01 sort`Swift._introSort (inout A,Swift.Range) -> () + 1233
    frame #5: 0x00000001000fc47f sort`Swift.sort (inout A) -> () + 607
    frame #6: 0x000000010013ea77 sort`partial apply forwarder for Swift.(sort (inout Swift.Array) -> ()).(closure #1) + 183
    frame #7: 0x000000010013eaf8 sort`partial apply forwarder for reabstraction thunk helper  from @callee_owned (@inout Swift.UnsafeMutableBufferPointer) -> (@unowned ()) to @callee_owned (@inout Swift.UnsafeMutableBufferPointer) -> (@out ()) + 56
    frame #8: 0x0000000100046c4b sort`Swift.Array.withUnsafeMutableBufferPointer (inout Swift.Array)((inout Swift.UnsafeMutableBufferPointer) -> B) -> B + 475
    frame #9: 0x00000001000fc5ad sort`Swift.sort (inout Swift.Array) -> () + 157
    frame #10: 0x00000001001cb465 sort`top_level_code + 1237 at main.swift:29
    frame #11: 0x00000001001cbdca sort`main + 42 at main.swift:0
    frame #12: 0x00007fff8aa9a5fd libdyld.dylib`start + 1

然后

(lldb) bt
* thread #1: tid = 0x5a00,Swift._Comparable.Self) -> Swift.Bool in conformance sort.MyStruct : Swift._Comparable + 27 at main.swift:20
    frame #2: 0x00000001000f449e sort`Swift._insertionSort (inout A,Swift.Range) -> () + 2958
    frame #3: 0x00000001000f730e sort`Swift._introSortImpl (inout A,Swift.Int) -> () + 1534
    frame #4: 0x00000001000f797d sort`Swift._introSortImpl (inout A,Swift.Int) -> () + 3181
    frame #5: 0x00000001000f6c01 sort`Swift._introSort (inout A,Swift.Range) -> () + 1233
    frame #6: 0x00000001000fc47f sort`Swift.sort (inout A) -> () + 607
    frame #7: 0x000000010013ea77 sort`partial apply forwarder for Swift.(sort (inout Swift.Array) -> ()).(closure #1) + 183
    frame #8: 0x000000010013eaf8 sort`partial apply forwarder for reabstraction thunk helper  from @callee_owned (@inout Swift.UnsafeMutableBufferPointer) -> (@unowned ()) to @callee_owned (@inout Swift.UnsafeMutableBufferPointer) -> (@out ()) + 56
    frame #9: 0x0000000100046c4b sort`Swift.Array.withUnsafeMutableBufferPointer (inout Swift.Array)((inout Swift.UnsafeMutableBufferPointer) -> B) -> B + 475
    frame #10: 0x00000001000fc5ad sort`Swift.sort (inout Swift.Array) -> () + 157
    frame #11: 0x00000001001cb465 sort`top_level_code + 1237 at main.swift:29
    frame #12: 0x00000001001cbdca sort`main + 42 at main.swift:0
    frame #13: 0x00007fff8aa9a5fd libdyld.dylib`start + 1

这证实了Airspeed’s answer的猜想,即使用内毒素
结合插入排序较小的范围.

如果数组具有少于20个元素,那么只有插入排序似乎被使用.
这可能表明从内部转换到的阈值
插入排序是20.

当然,实施可能会在将来发生变化.