[swift-evolution] [Discussion] Simplifying case syntax
erica at ericasadun.com
Wed Mar 1 14:17:47 CST 2017
> On Mar 1, 2017, at 11:46 AM, Matthew Johnson <matthew at anandabits.com> wrote:
>>> I agree that the ambiguity created by moving `let` outside the local =
>>> binding context is problematic. I alway place `let` immediately =
>>> alongside the binding for this reason. =20
>>> In design 2 do you disallow matching a value using an existing name? If =
>>> so, how do users match values bound to an existing name? Or is that =
>>> just not possible? I would oppose design 2 if it=E2=80=99s not =
>> It shadows, just like it currently does
> In that case I oppose design 2. If we're going to change this let's fix it and remove the ambiguity (from a reader's perspective when they don't know the rule).
I don't mind dropping design 2. It was added to the conversation just as we stopped
discussing this the first time. Was trying to pick up with all the conversation intact.
>>> Both syntax designs you propose are very concise, but they look like an =
>>> operator which can take any value with the appropriate type on the left =
>>> hand side. Unfortunately this isn=E2=80=99t the case (haha). I think =
>>> that is problematic. Did you consider this? If so, what is the =
>>> rationale for this choice?
>>> For example, a user might expect to be able to say:
>>> // match is a boolean that is true if the pattern matched and fast =
>>> let match =3D .success(let value) ~=3D result
>>> // we don=E2=80=99t know if `value` is bound here so we cannot allow the =
>>> above to be valid code.
>> Swift doesn't allow the results of conditional binding to be used as straightforward
>> Booleans as they must be bound into a scope. `guard` cheats.
> I understand that. What I'm saying is that I can't think of any other binary operator in Swift whose result cannot be assigned to a name. For that reason I am not convinced we should adopt the syntax you propose. This *is not* a normal binary operator expression so it shouldn't look like one.
How are you with design 1, my original design?
>> -- E
>>> href=3D"mailto:swift-evolution at swift.org" =
>>> class=3D"">swift-evolution at swift.org</a><br =
>>> class=3D"">https://lists.swift.org/mailman/listinfo/swift-evolution<br =
>>> class=3D""></div></blockquote></div><br =
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