Omitting unused closure parameters

[tim1724 (Tim Buchheim)]

@omochimetaru

This problem referred as technical reason here in 2016.
https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160118/007095.html

or here after the thread was imported into Discourse:

Proposal: Make $0 always refer to a closure’s first argument

Surprisingly, this code does not compile:     func foo(val: Int) { }     func bar(closure: (Int,Int) -> Void) {         closure(0, 1)     }     bar { foo($0) } // compiler error     bar { foo($1) } // just dandy     bar { foo($0 + $1) } // also works The compiler error is:     Cannot convert value of type (Int, Int) to expected argument type Int It appears that the meaning of $0 is overloaded: it can refer either to the tuple of all arguments, or to just the first argumen…