[swift-evolution] ternary operator ?: suggestion

[Charles Constant]

It's better, but it still seems a bit dry to me. I tried rewriting the
beginning. Is it better to start off like this?

*We are proposing a new “map” method. It directly addresses a “mapping”
problem that pops up in almost all Swift programs, and currently has no
elegant solution. The syntax we propose makes Swift code easier to read,
easier to write, and less buggy.*

*Here is an example of the problem, where we want to assign a string mapped
to an enum case:*

* let str:String*
* switch state {*
* case .Cold: *
* str = “Too cold”*
* case .Hot: *
* str = “Too hot”*
* default: *
* str = “Just right”*
* }*

*The syntax above does not elegantly express our intent. The “switch”
statement is designed for “flow control”, but aside from choosing a single
value, our example needs no “flow control”. Moreover, the ability to
execute unrelated statements inside the “switch” encourages buggy code. Use
of the “switch” statement for this task leads to bloated, confusing,
error-prone code.*


Do you like it? It's all pretty subjective, I suppose.


On Sat, Jan 16, 2016 at 8:51 PM, Craig Cruden <ccruden at novafore.com> wrote:

> Forgot to include the link so people don’t need to search:
>
>
> https://github.com/cacruden/swift-evolution/blob/master/proposals/0000-Pattern-Matching-Partial-Function.md
>
>
> On 2016-01-17, at 11:43:39, Craig Cruden <ccruden at novafore.com> wrote:
>
> Updated the the motivation clause - not sure I am 100% there yet - but
> hopefully closer.
>
> As well as a few minor updates to things like let on reduce example and
> clarifying that the partial closures can use the optional return keyword.
>
>
> On 2016-01-15, at 4:16:56, Charles Constant <charles at charlesism.com>
> wrote:
>
> Hi Craig,
>
> Well done, what you wrote looks pretty good to me. I had no trouble
> understanding the proposal. It's a good length, too - I think the shorter
> we can make it, the more appealing it is.
>
> The only section that I think needs improvement is "Motivation." I think
> we could sell it better. I know when I've read some of the other proposals,
> I do it in fairly cursory way.
> "Motivation" could be clearer for those of our peers who haven't followed
> the thread.
>
> The motivation, from my point of view:
> - the need to use a value from one domain, as a "key" to another is very
> common. The ternary is a special case of this, and for all it's flaws, it's
> a very popular expression in multiple languages
> - using the existing "switch" to do this is bloated (more so in Swift
> because you have to declare the variable before the switch statement)
> - using the existing "switch" to do this is less safe, because unrelated
> code can be inserted in the case statements
> - current alternatives to "switch" aren't good (e.g.: using a Dict has
> quirks that add the cognitive load)
> - this new "map" method can make code less verbose, easier to read, and
> safer
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> On Thu, Jan 14, 2016 at 11:23 AM, Craig Cruden <ccruden at novafore.com>
> wrote:
>
>> Paul,
>>
>> I tried to put my understanding on the latest proposal option into a
>> draft on github (instead of my usual BitBucket repo).
>>
>> Take a look at it and see if there is anything useable.
>>
>>
>> https://github.com/cacruden/swift-evolution/blob/master/proposals/0000-Pattern-Matching-Partial-Function.md
>>
>> Craig
>>
>> On 2016-01-11, at 14:17:09, Craig Cruden <ccruden at novafore.com> wrote:
>>
>> Ignore the last comment - tired and mistaken. :p
>>
>>
>> On 2016-01-11, at 14:16:01, Craig Cruden <ccruden at novafore.com> wrote:
>>
>> I just realized “cases” probably is not needed - if it see’s a comma
>> after case but before “:” then it is the concise form.
>>
>> If the switch / case can do that , the partial function case should be
>> able to do the same thing.
>>
>>
>> On 2016-01-11, at 13:23:19, Craig Cruden <ccruden at novafore.com> wrote:
>>
>> I have thought about it a bit more and I think this would cover all the
>> cases that interest me (in addition to others needs for a little more
>> conciseness on the most simple case).
>>
>> I also think we need to be clear that the “case” (or cases) and “default”
>> are is really just a partial function which in it’s entirety is really just
>> a complete function for used wherever a complete function (exhaustive) can
>> be passed (e.g. reduce, filter, etc.) - otherwise they might get confused
>> on why we are adding it to “map”.
>>
>> The optional where clause should also be part of the case clause as part
>> of the proposal.
>>
>> There would be no need for statement based “fallthrough”.
>>
>> You mentioned your proposal….  have you drafted a formal proposal draft?
>>
>>
>>
>> On 2016-01-10, at 12:41:03, Paul Ossenbruggen via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>
>> I agree that it would be really useful to keep things concise. I am going
>> to suggest again an idea I had in the past, it is also in my proposal,
>> which might work well for this problem. This might address the verbosity of
>> the “case” and at the same time make it obvious we are dealing with a
>> switch expression. So both would be valid:
>>
>> * let num = color.map {*
>>
>> * cases .Red: 100, *
>> * .Green:  200, *
>> * .Blue: 300*
>> * default: -1 *
>> * }*
>> * let num = color.map {*
>> * case .Red: 100*
>> * case .Green:  200 *
>> * case .Blue: 300*
>> * default: -1 *
>> * }*
>>
>>
>>
>>
>>
>>
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20160117/e7575072/attachment.html>