Related thread (which I wish got some clarifications from the core team): https://forums.swift.org/t/roadmap-for-and-state-of-single-element-tuple-types/13711
As far as I understand, single element tuples should be prevented in Swift.
The following program does not compile with (the default toolchain of) Xcode 9.4, as expected.
BUT with recent versions of the compiler (default toolchains of Xcode 10 beta 1 and beta 2, as well as recent dev snapshots), it does compile.
So we can define `t` to be of an instance of a (labeled) single-element tuple type, and use it as such.
But we cannot dump or print or otherwise access its type without getting (nonsensical) errors, and we cannot define its type explicitly, meaning the following will not compile:
Also, as a side note, the following program compiles with all versions of the compiler (including Xcode 9.4):
But I guess it shouldn't?