[swift-evolution] Deprecating Trailing Closures

Radosław Pietruszewski radexpl at gmail.com
Thu Mar 31 08:24:20 CDT 2016

> I think requring trailing closures to be @noescape would take away some very compelling use cases for them. In particular, you would lose the ability to use trailing closures for asynchronous code, like completion functions. I, for one, would be sad to lose those—they are often some of the largest, most block-like pieces of code that you put into a closure.

I, too, would be sad about that — but aside from a syntactic/stylistic choice, there aren’t any important-to-the-compiler semantics conveyed by the trailing closure, are there?

> At the same time, many of the things which people seem to think shouldn't be trailing closures, like `map` blocks, seem like good candidates for early returns or other control flow.

I *don’t* think `map` blocks should be able to control the outside scope. Map should map, that is transform. `forEach` should probably be able to do outside function control flow, and the use of trailing closure would be consistent with the Rule of Kevin.

> Basically, if you imagine a Venn diagram of "closures it would be useful to break out of early" and "closures you might want to use trailing closure syntax with", I don't think there's a particularly large amount of overlap between the two circles.

Aside from `map`, do you have other examples where there is no overlap?

— Radek

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