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

Jose Cheyo Jimenez cheyo at masters3d.com
Mon Apr 10 12:22:15 CDT 2017

> 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.

My understanding is that the slowdowns are produced when the inference has to take into account generics. If somebody is using lots of generics and overloads; I would hope they would know that this can slow down compile times. 
I am not sure how this can be communicated to the user other than showing a warning. 

> 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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