T(x)
where T is the name of a type. This syntax either coerces 'x' to the
type T or, failing that, enumerates the constructors of T and invokes
one of them.
Note that, syntactically, this coercion is syntactically identical to
a function application
f(x)
We distinguish these cases with a simple, syntax-based scheme: if the
'function' subexpression of the application can be trivially
determined to have metatype type, then we consider this a
construction. Otherwise, we assume that it's a function
application. This disallows some crazy coercions---e.g., those that
involve overloaded variables of metatype type---but should feel fairly
intuitive, and it keeps the constraint systems simpler.
Swift SVN r2802
