[swift-evolution] [Review] SE-0056: Allow trailing closures in `guard` conditions

Jeremy Pereira jeremy.j.pereira at googlemail.com
Mon Apr 4 09:49:29 CDT 2016

> On 3 Apr 2016, at 17:20, Haravikk via swift-evolution <swift-evolution at swift.org> wrote:
> Although I use trailing closures a lot less now, I think I’m a +1 anyway for consistency’s sake.
> I actually really like the idea of having trailing keywords in loops and if statements, these needn’t be required (except where a trailing closure is used) but for example it means I could do a fully natural language loop like:
> 	for eachValue in theValues do { … }

This is actually kind of bizarre. Here we are trying to invent new syntax so that the trailing closure can be used in if/while conditions and for sequences. However, there is already a perfectly good syntax for putting closures in these positions: put the closure in the parentheses of the function call. Are people really so desperate to use trailing closures everywhere that we have to add new keywords to the language? I don’t think they are.

> I like the consistency of every block having a kind of type (do, else, defer, catch etc.). 

That is a rabbit hole down which you probably shouldn't go. If we go down the route of blocks having a “type”, the current situation in Swift becomes somewhat inconsistent. I would argue that the `else` block on a `guard` is of a different type to the `else` block on an `if`. If anything, the `else` block of an `if` is closer to the `then` block. Also, would you allow the `do` block in a `for` or `while` to have a `catch` block following it? If not, then these blocks are different to the  existing bare `do` block. 

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