[swift-evolution] Making `.self` After `Type` Optional

[Joe Groff]

To keep progress going on this, I collected my thoughts from March's discussion into a draft proposal:

https://github.com/apple/swift-evolution/pull/299

-Joe

> On Mar 9, 2016, at 11:23 AM, Tanner Nelson via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Hello Swift Evolution members,
> 
> I would like to propose making `.self` After a Type optional when referencing Types in expressions.
> 
> Currently, to pass a Type to a function or method, it is sometimes required to add `.self` after the Type. This behavior is inconsistent as it is only required if the signature has more than one parameter. 
> 
> Here is a demonstration of the current inconsistency. 
> 
> ```swift
> func test<T: Any>(type: T.Type, two: String) {
>    print(type)
> }
> 
> func test<T: Any>(type: T.Type) {
>    print(type)
> }
> 
> test(Int.self)
> test(Int)
> 
> test(Int.self, two: "")
> test(Int, two: "") //Expected member name or constructor call after type name
>      ^~~
> ``` 
> 
> This has been confirmed as a bug, and the report can be seen here <https://bugs.swift.org/browse/SR-899>.
> 
> After a Twitter conversation with Joe Groff on the Swift team (https://twitter.com/jckarter/status/707287663586324481) it is determined that this requirement is due to difficulty disambiguating generics `Foo<T>` vs infix less-than operations `Foo < T`.
> 
> I propose to allow Types to be used in expressions without needing to explicitly reference `.self`. The motivation for this is as follows:
> 
> - Cleaner API
> - Consistent requirement is less confusing to developers
> - Disambiguation challenges should not result in more verbose code unless absolutely necessary
> 
> Here are some preliminary ideas for how this could be implemented:
> 
> - Require spaces around less than expressions and no spaces around generics
> - Require spaces around infix operators and no spaces around generics
> - Remove less than overload for comparing a type
> - (Your idea here)
> 
> A draft of an evolution document that provides more background can be viewed here <https://github.com/apple/swift-evolution/pull/197>. It has been preempted by a need for discussion in this mailing list. 
> 
> I am looking forward to hearing your feedback on this proposal.
> 
> Thank you,
> Tanner Nelson
> http://github.com/tannernelson
> 
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