[swift-evolution] [Pitch] Remove type-inference for stored property

[Sean Heber]

Well, I’m not really a beginner, but for me personally, the computer is here to help me do my work and to do some of the thinking for me. I really hate repeating myself when it comes to types - especially if the types get wordy (collections, etc). Swift is pretty good about it - but these warts stick out. The idea that we should make it *less* good at this really rubs me the wrong way. How many times have you seen lines of code like this in C++-ish/C#-ish languages:

Foo foo = new Foo();

Every time I see that sort of thing, I cringe a little.

IMO if you wanted to be super opinionated, the language would actually warn if you did this:

let foo: Foo = Foo()

And offer a fixit to:

let foo = Foo()

With no warning for things like this because you’re obviously doing something intentional:

let foo: FooSuperclass = Foo()

But I’d settle for no warnings and getting the inference to work in all contexts. :)

l8r
Sean


> On Apr 10, 2017, at 10:58 AM, Daniel Duan <daniel at duan.org> wrote:
> 
> It is helpful in the sense that it tells us what’s really inconsistent: beginner’s have to learn when inference is available when declaring their types. That’s story is sketchy.
>> On Apr 10, 2017, at 8:55 AM, Sean Heber <sean at fifthace.com> wrote:
>> 
>> This is not really a helpful comment, but: I kinda wish they did.
>> 
>> l8r
>> Sean
>> 
>>> On Apr 10, 2017, at 10:54 AM, Daniel Duan via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>> Neither of these works btw.
>>> 
>>> func bar(myString = “hello”)
>>> class Baz {
>>> let myString = { return “hello” }()
>>> }
>>> 
>>>> On Apr 9, 2017, at 11:26 PM, Jean-Daniel <mailing at xenonium.com> wrote:
>>>> 
>>>> I’m full -1 on this one. It will make the language inconsistent. How do you explain a new comer that type inference work in some case, but not in other cases, while in both the compiler is completely capable to define the type.
>>>> 
>>>> Why 
>>>> 
>>>> let myString = "hello" 
>>>> 
>>>> would be accepted but not 
>>>> 
>>>> class Foo {
>>>> 	let myString = "hello" 
>>>> }
>>>> 
>>>> 
>>>> 
>>>>> Le 10 avr. 2017 à 04:05, Daniel Duan via swift-evolution <swift-evolution at swift.org> a écrit :
>>>>> 
>>>>> I’m still not sure whether *I* want this. But here’s a proposal anyways: https://gist.github.com/dduan/5017a0b0f0880d014f4ce14c4ca7fb55
>>>>> 
>>>>>> On Apr 7, 2017, at 12:21 AM, Daniel Duan via swift-evolution <swift-evolution at swift.org> wrote:
>>>>>> 
>>>>>> Hi all,
>>>>>> 
>>>>>> In a discussion about inferring parameter types from default value, Slava brought up some performance problems caused by type inference for stored properties in side types:
>>>>>> 
>>>>>> https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20170313/033882.html
>>>>>> 
>>>>>> Towards the end, the post mentioned that some Swift team members contemplated requiring types for stored properties in type declarations. I think this idea deserves some more attention. Hence this last minute idea-floating.
>>>>>> 
>>>>>> In addition to solving a performance headache in implementation, there're always the general benefit of making type declartion more explicit and readable (clarity for reader should out-weigh pleasure of the author). Making the
>>>>>> language slightly more consistent (we are not inferring types for default parameter values in function anyways).
>>>>>> 
>>>>>> The cons for doing this are obvious too: the inference makes the language feels more friendly and is, undoubtedly, a beloved feature for many. This would be a source breaking change.
>>>>>> 
>>>>>> Just thought I'd float the idea to gather some quick reaction. What do y'all think?
>>>>>> 
>>>>>> Daniel Duan
>>>>>> _______________________________________________
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>>>>>> swift-evolution at swift.org
>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>>> 
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