[swift-evolution] Lambda function syntax

Andrey Tarantsov andrey at tarantsov.com
Tue Dec 22 20:52:46 CST 2015

> foo.map( bar => bar.boz) // single line

Well how important is it to use () instead of {} here?

If you make it

foo.map { bar => bar.boz }

then it's like it is now, but with "in" replace by "=>".

> foo.map { (x, y) => x * 5 + y }

I actually like the bare version:

foo.map { x, y => x * 5 + y }

but not in your example (here it looks atrocious). Take this real code, though:

        constrain(topBlock, tableView, view) { top, tbl, sup in
            top.left  == sup.left + horizPadding
            top.right == sup.right - horizPadding
            top.top   == sup.top  + topPadding

            tbl.top    == top.bottom + 16
            tbl.bottom == sup.bottom

            tbl.left  == sup.left + horizPadding - horizTableHang
            tbl.right == sup.right - horizPadding + horizTableHang

I think the lack of parens is beneficial in reducing the visual noise here.

> And yes, I certainly would prefer `=>` rather than `in`.

It seems like the community can actually agree on this.

Does anyone know if it has any parsing problems / grammar implications right now? 

> I think a big problem with `in` is that it’s textual, and doesn’t provide a clear visual separation from keywords/names at the start of the body or the end of the type specifier.

Yes, agreed. “Not delimited enough”.

> (Are the [parentheses] around `bar` in your example required? I’m ambivalent to them.)

No, they are not, as shown above.

> To be clear, I’m still not a fan of the Ruby syntax. I think it makes the parsing easier for a compiler but harder for a human…

Depends on the human. To this specific human, the Ruby-style one is the easiest to parse (and mind you, I had very limited experience with Ruby compared to other languages, so it's not just being used to it, but rather an honest love and preference).


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