[swift-evolution] Enable omitting `let` for constant declarations

[Yuta Koshizawa]

> Radosław

Hi. I found Stephen Celis proposed exactly same notations in the
thread "Mutability inference". I guess it is what you talked about.

> let a: String = "string"
> b: String = "string" // short-hand avoids let
> b := "string" // shorter-hand

But it seems that it was not well discussed, and I think it is worth
discussing it.

> Macko

Thanks!

-- Yuta


2016-04-03 16:23 GMT+09:00 Macko Jeffrey <macko.jeffrey at gmail.com>:
> I love your propositions Yuta.
>
> ---
> Macko Jeffrey
>
>> Le 1 avr. 2016 à 20:58, Yuta Koshizawa via swift-evolution <swift-evolution at swift.org> a écrit :
>>
>> Did you mean the thread "Mutability inference"? What I talked about is
>> different from it. I am against the idea of "Mutability inference".
>>
>> What I talked about is just enabling to omit `let` for constant
>> declarations. It distinguishes the following three explicitly.
>>
>>> - assignment
>>> - declaration of a constant
>>> - declaration of a mutable variable
>>
>> `:=` makes it possible to distinguish assignments and constant declarations.
>>
>> -- Yuta
>>
>>
>> 2016-04-01 23:55 GMT+09:00 Radosław Pietruszewski <radexpl at gmail.com>:
>>> I can’t easily find it, but there’s been at least one thread proposing this exact thing, and there was very little interest in the proposal.
>>>
>>> TL;DR is that Swift *by design* wants to make the difference between these three concepts:
>>>
>>> - assignment
>>> - declaration of a constant
>>> - declaration of a mutable variable
>>>
>>> as explicit and obvious as possible.
>>>
>>> — Radek
>>>
>>>> On 01 Apr 2016, at 13:58, Yuta Koshizawa via swift-evolution <swift-evolution at swift.org> wrote:
>>>>
>>>> I think it would be good if the following three declarations were equivalent
>>>>
>>>> let a: Int = 42
>>>> a: Int = 42
>>>> a := 42
>>>>
>>>> and also the following two were.
>>>>
>>>> let a: Int
>>>> a: Int
>>>>
>>>> Then constant declarations become shorter than variable declarations.
>>>> It encourages people to use constants in preference to variables.
>>>>
>>>> It also prevents repeating `let` for property declarations and makes
>>>> type declarations simpler.
>>>>
>>>> struct Person {
>>>>   firstName: String
>>>>   lastName: String
>>>>   age: Int
>>>> }
>>>>
>>>> Omitting `let` is consistent with that we don't write `let` for
>>>> arguments of functions and iterated values in for-in loops.
>>>>
>>>> Not `=` but `:=` for type inferences because `=` cannot distinguish
>>>> whether it means a constant declaration or an assignment to a variable
>>>> declared in an outer scope. I think `:=` is a natural notation for
>>>> type inferences because omitting the type from `a: Int = 42` makes
>>>> `a:= 42`. Because I have not strictly checked if it can be parsed in
>>>> Swift properly, it may have some other parsing issues.
>>>>
>>>> What do you think about it?
>>>>
>>>> -- Yuta
>>>> _______________________________________________
>>>> swift-evolution mailing list
>>>> swift-evolution at swift.org
>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-evolution