cfcast.cc

namespace base {
  namespace mac {

    template<typename T> T CFCast(CFTypeRef cf_val) {
      if (!cf_val) return NULL;

      if (CFGetTypeID(cf_val) == CFStringGetTypeID()) {
        return (CFStringRef)cf_val;
      }

      return NULL;
    }

  }  // namespace mac
}  // namespace base

cfcast.h

namespace base {
  mac {
    template<typename T> T CFCast(CFTypeRef cf_val);
  }
}

err_output.txt

  LINK(target) out/Debug/base_unittests
Undefined symbols:
  "__ZN4base3mac6CFCastIPK10__CFStringEET_PKv", referenced from:
      __ZN29CFCastTest_ToCFStringRef_Test8TestBodyEv in foundation_util_unittest.o
  "__ZN4base3mac6CFCastIPK14__CFDictionaryEET_PKv", referenced from:
      __ZN33CFCastTest_ToCFDictionaryRef_Test8TestBodyEv in foundation_util_unittest.o
ld: symbol(s) not found
clang: error: linker command failed with exit code 1 (use -v to see invocation)
  LINK(target) out/Debug/base_unittests: Finished