[cfe-dev] Clang (3.1 and 3.2): __attribute__((overloadable)) and enum types.

[Lizunov, Andrey E]

Thank you for the answer,

So, it is not a bug but a standard behavior in C unlike of C++.
To make it work a variable of enum type should be defined.

$ cat try.c
#include <stdio.h>

typedef enum {ONE = 1} One;
typedef enum {TWO = 2} Two;

__attribute__((overloadable)) void foo(One arg){
  printf("One = %d\n", arg);
}
__attribute__((overloadable)) void foo(Two arg){
  printf("Two = %d\n", arg);
}

int main() {
  One one = ONE;
  Two two = TWO;

  foo(one);
  foo(two);
  return 0;
}

bash-4.1$ clang -x c try.c; ./a.out
One = 1
Two = 2

BR,
Andrey Lizunov

From: Ólafur Waage [mailto:olafurw at gmail.com]
Sent: Friday, August 02, 2013 5:02 PM
To: Lizunov, Andrey E
Cc: cfe-dev at cs.uiuc.edu
Subject: Re: [cfe-dev] Clang (3.1 and 3.2): __attribute__((overloadable)) and enum types.

// bleh.cpp
#include <iostream>

enum class One : int {DUMMY_1 = 1};
enum class Two : unsigned int {DUMMY_2 = 1};
enum class Three : char {DUMMY_3 = 1};

void foo(One)
{
    std::cout << "One" << std::endl;
}
void foo(Two)
{
    std::cout << "Two" << std::endl;
}
void foo(Three)
{
    std::cout << "Three" << std::endl;
}

int main()
{
    foo(One::DUMMY_1);
    foo(Two::DUMMY_2);
    foo(Three::DUMMY_3);
    return 0;
}

//

$ clang++ -std=c++11 bleh.cpp -o bleh
$ ./bleh
One
Two
Three

On Fri, Aug 2, 2013 at 12:57 PM, Ólafur Waage <olafurw at gmail.com<mailto:olafurw at gmail.com>> wrote:
Since enums in C are just named integers, they are all of the same type. So it would be the same as doing three functions with int as the argument.


On Fri, Aug 2, 2013 at 12:29 PM, Lizunov, Andrey E <andrey.e.lizunov at intel.com<mailto:andrey.e.lizunov at intel.com>> wrote:
Hello,

I was trying to use  __attribute__((overloadable)) for functions accepting enumerated types but hadn’t succeeded so far.
Clang 3.1 and 3.2 failed to compile the following example.
/* clang -x c foo.cpp */
typedef enum __One {DUMMY_1} One;
typedef enum {DUMMY_2} Two;
enum Three {DUMMY_3};

__attribute__((overloadable)) void foo(One);
__attribute__((overloadable)) void foo(Two);
__attribute__((overloadable)) void foo(enum Three);

int main()
{
  foo(DUMMY_1);
  return 0;
}
Providing me with the following error message:
$ clang -x c foo.cpp
foo.cpp:22:3: error: call to 'foo' is ambiguous
  foo(DUMMY_1);
  ^~~
foo.cpp:16:36: note: candidate function
__attribute__((overloadable)) void foo(One);
                                   ^
foo.cpp:17:36: note: candidate function
__attribute__((overloadable)) void foo(Two);
                                   ^
foo.cpp:18:36: note: candidate function
__attribute__((overloadable)) void foo(enum Three);
                                   ^
1 error generated.
While with “-x c++” both versions of Clang compiled it successfully (failed to link though).

According to http://clang.llvm.org/docs/LanguageExtensions.html#function-overloading-in-c overloadable attribute is an analogue for C++ function overloading in C.
So, is it a bug in the Clang or I didn’t understand/consider something?


BR,
Andrey Lizunov


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