Open Radar

 
Summary:
A Dictionary extension with a where clause to restrict the input parameter to be a Sequence of tuples of the same (KeyType, ValueType) as that Dictionary itself.

The compiler matches against any sequence. The code produced for the extension correctly matches against KeyType only.

Steps to Reproduce:
Copy & paste this into Swift (xcrun swift or Xcode):

extension Dictionary {
	mutating func merge <E: Element, S: Sequence where S.GeneratorType.Element == Element> (seq: S) {
		var gen = seq.generate()
		while let n: E = gen.next() {
			self[n.0] = n.1
		}
	}
}
 
var dict = [0:0]
let array = [1.0,2.0,3.0]
dict.merge(array)
println(dict)
let more = [1,2,3]
dict.merge(more)
println(dict)
dict.merge(again)
println(dict)

Expected Results:
Should give a compiler error on both dict.merge() lines, since the Sequences GeneratorType.Elements are Int or Double, not Dictionary.Element (aka (KeyType,ValueType)).

Actual Results:
Runs with no error, prints out [0: 0, 1: 140735543552768, 2: 140735543552768, 3: 140735543552768]

Note that the first dict.merge() call does nothing.
Note garbage values for the second call.