c++ - GoogleTest 无法使用自定义比较运算符

Question

我想在 Google Test 中对我的 Word 结构进行简单测试。为了使测试代码更简单和更短，我决定编写一个比较运算符(尽管我并不真的需要一个)并且只使用 ASSERT_EQ，根据 the primer .尽管一切看起来都很好，但我收到编译器错误:

/* Word.h */
namespace tgs {

struct Word {
    //something here
    Word();
    virtual ~Word();
    bool operator== (Word& rhs);
};
}

/* Word.cpp */
namespace tgs {
bool Word::operator== (Word& rhs){
  return true; //there are actual member comparisons here
}
}


/* TextAreaShould_test.cc */
TEST_F(TextAreaShould, DoSomething) {
  Word w1, w2;

  if(w1 == w2){ //compiles and runs ok
    0;
  }
  ASSERT_EQ(w1, w2); //produces following error
}

编译错误:

[ 86%] Building CXX object CMakeFiles/tests/TextAreaShould.test.dir/tests/TextAreaShould_test.cc.o
/usr/bin/c++    -I/home/nietaki/zpp/TheGameShow_build -I/home/nietaki/zpp/TheGameShow -I/home/nietaki/zpp/TheGameShow/google_mock/include -I/home/nietaki/zpp/TheGameShow/google_mock/gtest/include -I/usr/local/include   -o CMakeFiles/tests/TextAreaShould.test.dir/tests/TextAreaShould_test.cc.o -c /home/nietaki/zpp/TheGameShow/tests/TextAreaShould_test.cc
In file included from /home/nietaki/zpp/TheGameShow/tests/TextAreaShould_test.cc:8:
/home/nietaki/zpp/TheGameShow/google_mock/gtest/include/gtest/gtest.h: In function ‘testing::AssertionResult testing::internal::CmpHelperEQ(const char*, const char*, const T1&, const T2&) [with T1 = tgs::Word, T2 = tgs::Word]’:
/    home/nietaki/zpp/TheGameShow/google_mock/gtest/include/gtest/gtest.h:1363:   instantiated from ‘static testing::AssertionResult testing::internal::EqHelper<lhs_is_null_literal>::Compare(const char*, const char*, const T1&, const T2&) [with T1 = tgs::Word, T2 = tgs::Word, bool lhs_is_null_literal = false]’
/home/nietaki/zpp/TheGameShow/tests/TextAreaShould_test.cc:112:   instantiated from here
/home/nietaki/zpp/TheGameShow/google_mock/gtest/include/gtest/gtest.h:1326: error: no match for ‘operator==’ in ‘expected == actual’
/home/nietaki/zpp/TheGameShow/renderer/textarea/Word.h:25: note: candidates are: bool tgs::Word::operator==(tgs::Word&)

我还尝试将比较运算符放在类之外，而不是作为成员，但这似乎并没有太大的区别。我尝试按照 Primer 做所有事情，但也许有些地方不对。

Answer 1

比较运算符不会更改任何参数，因此它可以是 const，如 Gooogle Test 使用的那样:

struct Word {

    Word();
    virtual ~Word();
    bool operator== (const Word& rhs) const;
};

...一切正常。