<div dir="ltr"><div>No problem Erica, I find this to be pretty subtle!</div><div><br></div><div>That's definitely how static versions of instance methods work today, and it does it's job pretty well! My suggestion to flip the arguments is a bid to increase the readability and re-usability of these methods without changing any of the real semantics.</div><div><br></div><div>Here's how we can do it manually in order to see the benefits. The following function:</div><div><br></div><div>func flip <A, B, C> (f: A -> B -> C) -> B -> A -> C {</div><div> return { b in { a in f(a)(b) } }</div><div>}</div><div><br></div><div>simply converts `A -> B -> C` to `B -> A -> C`, i.e. flips its arguments. Let's use it make a version of `UIView.removeFromSuperview` that I think is more understandable:</div><div><br></div><div>extension UIView {</div><div> @nonobjc static let _removeFromSuperview = flip(UIView.removeFromSuperview)</div><div>}</div><div><br></div><div>(ignore that @nonobjc, it's only necessary cause Swift is trying to generate a dynamic accessor)</div><div><br></div><div>With this method your code example becomes</div><div><br></div><div>v.subviews.forEach(UIView._removeFromSuperview())</div><div><br></div><div>To me this reads: for each subview of `v`, apply the action `UIView._removeFromSuperview()`. Compare this to the equivalent with today's static method:</div><div><br></div><div>v.subviews.map(UIView.removeFromSuperview).forEach{ $0() }</div><div><br></div><div>This is read as: map the subviews of `v` into an array of actions, and then invoke those actions.</div><div><br></div><div>The benefits of this flip are easier to see with different examples, because I agree with Stephen that it's hard to beat a simple `v.subviews.forEach { $0.removeSuperView() }` in this particular example.</div><div><br></div><div>If static methods had their arguments flipped, we'd be able to easily construct functions like `CGRect.insetBy(10.0, 10.0)` and `CGRect.offsetBy(-20.0, 10.0)`. These are now free functions without any mention to a specific rectangle. We could compose them to get a function that simulataneously insets and translates, all without mentioning a rectangle. With today's static methods we'd have to apply `flip` to each one, i.e. `flip(CGRect.insetBy)(10.0, 10.0)`.</div><div><br></div><div>This becomes very powerful with constructing data pipelines that describe how to transform data without ever actually mentioning the data. There are quite a few examples of things like this in Cocoa. A nice one is Core Image, in which you can build a pipeline of filters that you can feed images into.</div><div><br></div><div><br></div><div><br></div><div><br></div><br><div class="gmail_quote"><div dir="ltr">On Sun, Mar 13, 2016 at 3:45 PM Erica Sadun <<a href="mailto:erica@ericasadun.com">erica@ericasadun.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><div>I'm probably missing the point here, so apologize in advance. Instead of reducing a function with an n-arity set of arguments to a partially applied function with (m|m<n)-arity set of arguments, it's building a functional application and applying that to an arbitrary receiver.</div><div><br></div><div><span style="white-space:pre-wrap"> </span>`UIView.removeFromSuperview(receiver) `</div><div><br></div><div>defines</div><div><br></div><div><span style="white-space:pre-wrap"> </span>`receiver.removeFromSuperview`</div><div><br></div><div>which can then be applied with whatever arguments, () in this case.</div><div><div><br></div><div><span style="white-space:pre-wrap"> </span>`UIView.removeFromSuperview(receiver)()` aka `receiver.removeFromSuperview()`</div></div><div><br></div><div>With mapping, you can do:</div><div><br></div><div><div style="margin:0px;font-size:18px;line-height:normal;font-family:Menlo"><span style="color:#bb2ca2">let</span> v = <span style="color:#703daa">UIView</span>()</div><div style="margin:0px;font-size:18px;line-height:normal;font-family:Menlo;color:rgb(61,29,129)"><span style="color:#000000">(</span><span style="color:#272ad8">1</span><span style="color:#000000">...</span><span style="color:#272ad8">5</span><span style="color:#000000">).</span>forEach<span style="color:#000000">{</span><span style="color:#bb2ca2">_</span><span style="color:#000000"> </span><span style="color:#bb2ca2">in</span><span style="color:#000000"> </span><span style="color:#4f8187">v</span><span style="color:#000000">.</span>addSubview<span style="color:#000000">(</span><span style="color:#703daa">UIView</span><span style="color:#000000">())}</span></div><div style="margin:0px;font-size:18px;line-height:normal;font-family:Menlo;color:rgb(61,29,129)"><span style="color:#000000"><br></span></div><div style="margin:0px;font-size:18px;line-height:normal;font-family:Menlo;color:rgb(61,29,129)"><div style="margin:0px;line-height:normal;color:rgb(0,132,0)">// You can apply each subview as a receiver, returning a function</div><div><span style="color:rgb(187,44,162)">let</span><span style="color:rgb(0,0,0)"> applied = </span><span style="color:rgb(79,129,135)">v</span><span style="color:rgb(0,0,0)">.</span><span style="color:rgb(112,61,170)">subviews</span><span style="color:rgb(0,0,0)">.</span>map<span style="color:rgb(0,0,0)">(</span><span style="color:rgb(112,61,170)">UIView</span><span style="color:rgb(0,0,0)">.</span>removeFromSuperview<span style="color:rgb(0,0,0)">) </span></div></div><div style="margin:0px;font-size:18px;line-height:normal;font-family:Menlo;color:rgb(0,132,0)">// [(Function), (Function), (Function), (Function), (Function)]</div><div style="margin:0px;font-size:18px;line-height:normal;font-family:Menlo;color:rgb(0,132,0)"><br></div><div style="margin:0px;font-size:18px;line-height:normal;font-family:Menlo;color:rgb(0,132,0)"><div style="margin:0px;line-height:normal">// And then you an execute them in forEach</div><div><span style="color:rgb(61,29,129)">print</span><span style="color:rgb(0,0,0)">(</span><span style="color:rgb(79,129,135)">v</span><span style="color:rgb(0,0,0)">.</span><span style="color:rgb(112,61,170)">subviews</span><span style="color:rgb(0,0,0)">.</span><span style="color:rgb(112,61,170)">count</span><span style="color:rgb(0,0,0)">) </span>// 5</div></div><div style="margin:0px;font-size:18px;line-height:normal;font-family:Menlo;color:rgb(61,29,129)"><span style="color:#4f8187">v</span><span style="color:#000000">.</span><span style="color:#703daa">subviews</span><span style="color:#000000">.</span>map<span style="color:#000000">(</span><span style="color:#703daa">UIView</span><span style="color:#000000">.</span>removeFromSuperview<span style="color:#000000">).</span>forEach<span style="color:#000000">{$0()}</span></div><div style="margin:0px;font-size:18px;line-height:normal;font-family:Menlo;color:rgb(112,61,170)"><span style="color:#3d1d81">print</span><span style="color:#000000">(</span><span style="color:#4f8187">v</span><span style="color:#000000">.</span>subviews<span style="color:#000000">.</span>count<span style="color:#000000">) </span><span style="color:#008400">// 0</span></div></div><div><span style="color:#008400"><br></span></div><div>The whole map/forEach could be defined down to apply in a possible language extension, as I mentioned before.</div><div><br></div><div>-- E, who apologizes for really not getting this</div></div><div style="word-wrap:break-word"><div><br></div><div><br></div><div><blockquote type="cite"><div>On Mar 13, 2016, at 1:21 PM, Brandon Williams <<a href="mailto:mbw234@gmail.com" target="_blank">mbw234@gmail.com</a>> wrote:</div><br><div><div dir="ltr"><div>I think this highlights some of the confusion around the current curried convention. Void methods are curried as A -> () -> (), which means you would use it like:</div><div><br></div><div><div>UIView.removeFromSuperview # => UIView -> () -> ()</div><div>UIView.removeFromSuperview(view) # => () -> ()</div><div>UIView.removeFromSuperview(view)() #> ()</div></div><div><br></div><div>I find this confusing because removeFromSuperview reads as an action, yet UIView.removeFromSuperview(view) does not perform the action but rather is an action itself that requires a further invocation ().</div><div><br></div><div>With arguments flipped we would have:</div><div dir="ltr"><div><br></div><div><div>UIView.removeFromSuperview # => () -> UIView -> ()</div><div>UIView.removeFromSuperview() # => UIView -> ()</div><div>UIView.removeFromSuperview()(view) #> ()</div></div><div><br></div><div>It now reads to me that UIView.removeFromSuperview() is the action that will do the removing, and UIView.removeFromSuperview()(view) is applying the action to a view.</div><div><br></div><div>I don’t advocate using removeFromSuperview in this manner, but if one were to I believe the latter convention is easier to reason about without having to look up types in a playground (as I had to do a few times to write this :P)</div><br><br><div class="gmail_quote"><div dir="ltr">On Sun, Mar 13, 2016 at 1:50 PM Erica Sadun via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><br>
> On Mar 13, 2016, at 11:30 AM, Stephen Celis <<a href="mailto:stephen.celis@gmail.com" target="_blank">stephen.celis@gmail.com</a>> wrote:<br>
><br>
>> On Mar 13, 2016, at 1:18 PM, Erica Sadun <<a href="mailto:erica@ericasadun.com" target="_blank">erica@ericasadun.com</a>> wrote:<br>
>><br>
>> Since removeFromSuperview doesn't take a UIView argument, it sounds like what you're looking for is<br>
>> something that acts like "apply", to apply a lambda/closure/selector/whatever to each member of a collection.<br>
>><br>
>> view.subviews.apply(UIView.removeFromSuperview)<br>
>><br>
>> -- E<br>
><br>
> This is what `forEach` currently does with the existing curried static syntax, right?<br>
><br>
> I was more interested in the implications of an example brought up in the OP:<br>
><br>
> frames.map(CGRect.insetBy(-10, -10))<br>
><br>
> - Stephen<br>
<br>
forEach currently does f(x).<br>
apply would do x.f()<br>
<br>
-- E<br>
<br>
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