How do you test functions and closures for equality?

closures swift equality
Jessy picture Jessy · Jun 9, 2014 · Viewed 12.8k times · Source

The book says that "functions and closures are reference types". So, how do you find out if the references are equal? == and === don't work.

func a() { }
let å = a
let b = å === å // Could not find an overload for === that accepts the supplied arguments

Answer

drewag picture drewag · Sep 5, 2014

Chris Lattner wrote on the developer forums:

This is a feature we intentionally do not want to support. There are a variety of things that will cause pointer equality of functions (in the swift type system sense, which includes several kinds of closures) to fail or change depending on optimization. If "===" were defined on functions, the compiler would not be allowed to merge identical method bodies, share thunks, and perform certain capture optimizations in closures. Further, equality of this sort would be extremely surprising in some generics contexts, where you can get reabstraction thunks that adjust the actual signature of a function to the one the function type expects.

https://devforums.apple.com/message/1035180#1035180

This means that you should not even try to compare closures for equality because optimizations may affect the outcome.

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