C++ name scoping question


I’m hoping a C++ language expert can help me with scoping rules for named function parameters.

As background, I’d like to allow named function parameters in non-function declarations (such as function-pointer-typed variables) to be referenced in attribute expressions. Currently, attempting to do so results in “use of undeclared identifier”. However, I’m not even sure the standard allows me to do this, let alone what assumptions any patch to clang might run afoul of.

Consider the declaration:

void (*pFn)(int x);

Reading the standard (specifically, I’m looking at C++11 draft N4527), I gather that:

​1. pFn is not a “function declarator”. I didn’t see a clear definition of this, but I assume function and variable are mutually exclusive descriptions of a declarator, and that this would be a variable declarator.

  1. According to [basic.scope.proto] (3.3.4), named parameters inside function declarators which are not also definitions have function prototype scope, but this only applies to function declarators. I do not find a scoping rule that would apply to x in my pFn example, assuming point 1 is correct.

This seems like x has no applicable scoping rule and you shouldn’t be able to reference it. However, I note the following declaration is accepted as valid C++11:

auto (*pSum)(int x, double y) → decltype(x + y);

I’d appreciate any help understanding what portions of the standard apply to my examples and how to interpret them, and whether the standard in fact allows me to place an attribute on pFn which references x.


David Fontaine