SE-0216: User-defined dynamically callable types

[dan-zheng]

@beccadax

One last comment: if the core team does adopt SE-0216, I hope it at least considers removing dynamicCall(withArguments:) (and probably giving its name to the withKeywordArguments: form). The justifications given for including it don't seem very strong, and about 10% of the patch seems to be devoted to supporting it.

For the record: the motivation for separating the withArguments: and withKeywordArguments: methods is to disallow keyword-argument-calls for languages that don't support keywords. The example used in the proposal is JavaScript.
For languages without keyword arguments, defining a withKeywordArguments: method would be unnatural and a "no argument labels" precondition would be required at run time.