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

[Tanner Nelson]

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