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

[Daniel Duan]

I guess I'm using the word "export" loosely. Often times I find myself reading type signatures in my own codebase either because it's written by someone else on my team or by myself long time ago. I think open-source library users have the same problem. Exposure to a particular local variable is less likely.

Daniel Duan
Sent from my iPhone

> On Apr 10, 2017, at 9:16 AM, Matthew Johnson <matthew at anandabits.com> wrote:
> 
> 
>> On Apr 10, 2017, at 11:11 AM, Daniel Duan via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> 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.
> 
> When a declaration is exported outside a module whoever is reading it isn’t reading the source directly.  They are reading documentation or a generated header of some kind.  The annotation can easily be added by tools that produce these.
> 
>> 
>>> 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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>>>> 
>>> 
>> 
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