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

[Jaden Geller]

> On Apr 7, 2017, at 4:07 AM, Vladimir.S via swift-evolution <swift-evolution at swift.org> wrote:
> 
> On 07.04.2017 10:21, Daniel Duan via swift-evolution 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?
> 
> Although it seems like only an implementation-side problem(i.e. "let's just improve implementation"), I see a benefits to require type for stored property *if* it is not obvious what the type is for *reader*. I.e. if we have something like this, I don't think we should require a type:
> struct S {
>  var x = 0
> }

I think there is value in requiring a type annotation there. For example, this bug would be avoided: https://twitter.com/benjaminencz/status/851892622213783552

> 
> but I do think it will be better to require a type in such cases :
> 
> struct S{
>  var x = something(SomeType(), 123, "123") // can be generic func
> }
> 
> 
> 
>> 
>> Daniel Duan _______________________________________________
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>> 
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