Stop pessimizing print performance for no reason.

lattner · tkremenek · commit a10a715c02d8 · 2018-01-24T14:15:44.000-08:00
As pointed out in Ole Begeman's blog: https://oleb.net/blog/2016/09/playground-print-hook/ The playground print hook is being initialized a a non-null noop hook, which causes the fast paths in the print functions to be unused, and forcing the creation of a tee stream for things that have nothing to do with playgrounds. It is sad that no one noticed this...
diff --git a/stdlib/public/core/OutputStream.swift b/stdlib/public/core/OutputStream.swift
@@ -624,7 +624,7 @@ extension Unicode.Scalar : TextOutputStreamable {
 }
 
 /// A hook for playgrounds to print through.
-public var _playgroundPrintHook : ((String) -> Void)? = {_ in () }
+public var _playgroundPrintHook : ((String) -> Void)? = nil
 
 @_fixed_layout // FIXME(sil-serialize-all)
 @_versioned // FIXME(sil-serialize-all)

Original file line number	Diff line number	Diff line change
`@@ -624,7 +624,7 @@ extension Unicode.Scalar : TextOutputStreamable {`
`624`	`624`	`}`
`625`	`625`
`626`	`626`	`/// A hook for playgrounds to print through.`
`627`		`-public var _playgroundPrintHook : ((String) -> Void)? = {_ in () }`
	`627`	`+public var _playgroundPrintHook : ((String) -> Void)? = nil`
`628`	`628`
`629`	`629`	`@_fixed_layout // FIXME(sil-serialize-all)`
`630`	`630`	`@_versioned // FIXME(sil-serialize-all)`