dnedrow · May 15, 2018 14:46 · Nov 5, 2016 · Nov 5, 2016
diff --git a/doOnce.swift b/doOnce.swift
@@ -21,3 +21,6 @@ doOnce() // does not print
 
 // So is this good Swift that readers should simply learn to understand, or is it over-clever Swift
 // that has a better answer that is both idempotent and threadsafe?
+
+// I know the docs suggest just "evaluating a var with _ =" but that seems horrible compared to having a clear
+// function-call syntax.
diff --git a/doOnce.swift b/doOnce.swift
@@ -0,0 +1,23 @@
+// Swift3 gets rid of dispatch_once and recommends replacing it with a lazy global.
+// That's very straightforward when dispach_once is used to initialize something, but
+// isn't an exact match when you want something to execute once, and then become a noop
+// in a thread-safe way.
+
+// The following approach seems completely "correct" and I guess actually a bit elegant,
+// if by "elegant" you mean "terse and not immediately obvious to the reader, which makes
+// you look very clever."
+
+var doOnce: () -> Void = {
+    // The side effect that should only happen once
+    print("Running once, I hope")
+
+    // A dummy function that's evaluated every time we're accessed
+    return {}
+}()
+
+doOnce() // Prints
+doOnce() // does not print
+doOnce() // does not print
+
+// So is this good Swift that readers should simply learn to understand, or is it over-clever Swift
+// that has a better answer that is both idempotent and threadsafe?