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

[Daniel Duan]

I’m not questioning the value of type inference in general. Just that there are practical implications when we want more of them. There’s a difference in inferencing type declaration properties and local variables: the former is more likely to be exported and read by others. These arguments are all in the draft proposal.

> On Apr 10, 2017, at 9:07 AM, Sean Heber <sean at fifthace.com> wrote:
> 
> 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
>>>>>>> _______________________________________________
>>>>>>> swift-evolution mailing list
>>>>>>> swift-evolution at swift.org
>>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>>>> 
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>>>>> 
>>>> 
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>> 
>