swift234

Make sure we to only combine casts we know will succeed.

I don't think we can sneek one by the compiler but lets be conservative.

  1> import Foundation
  2> struct Unbridged {}
  3> var a : [Unbridged] = []
a: [Unbridged] = 0 values
  4> a as NSArray
repl.swift:4:3: error: '[Unbridged]' is not convertible to 'NSArray'
a as NSArray
~^~~~~~~~~~
  4> func test<T>(a :[T]) -> NSArray { return a as NSArray }
repl.swift:4:44: error: '[T]' is not convertible to 'NSArray'

Swift SVN r26259