Proposed resolution (January, 2019):

Consider:

  int x = (int()) + 5; 

This is ill-formed, because 9.3.3 [dcl.ambig.res] paragraph 2 specifies:

An ambiguity can arise from the similarity between a function-style cast and a type-id. The resolution is that any construct that could possibly be a type-id in its syntactic context shall be considered a type-id.

and thus int() is interpreted as a type-id instead of as a function-style cast, so this is an ill-formed cast to a function type.

This seems to be the wrong disambiguation for all cases where there is a choice between a C-style cast and a parenthesized expression: in all those cases, the C-style cast interpretation results in a cast to a function type, which is always ill-formed.

Further, there is implementation divergence in the handling of this example:

  struct T { int operator++(int); T operator[](int); };
  int a = (T()[3])++; // not a cast

EWG 2022-11-11

This is tracked in github issue cplusplus/papers#1376.