如何让自定义运营商==使用Google Test？

Question

我在使用PCL和Google Test(GTest)的自定义重载'=='运算符时遇到问题

#include <pcl/point_types.h>
namespace pcl { struct PointXYZ; }

bool operator==(pcl::PointXYZ p1, pcl::PointXYZ p2) {return p1.x-p2.x<.1;}
#include <gtest/gtest.h>

TEST(Foo, bar) {
  pcl::PointXYZ a{2,3,4};
  pcl::PointXYZP b{2,3,4};
  EXPECT_EQ(a,b); // Compile error no match for operator==
}

int main(int argc, char **argv){
  testing::InitGoogleTest(&argc, argv);
  return RUN_ALL_TESTS();
}

我得到的错误是:

|| /usr/include/gtest/gtest.h: In instantiation of 'testing::AssertionResult testing::internal::CmpHelperEQ(const char*, const char*, const T1&, const T2&) [with T1 = pcl::PointXYZ; T2 = pcl::PointXYZ]':
/usr/include/gtest/gtest.h|1361 col 23| required from 'static testing::AssertionResult testing::internal::EqHelper<lhs_is_null_literal>::Compare(const char*, const char*, const T1&, const T2&) [with T1 = pcl::PointXYZ; T2 = pcl::PointXYZ; bool lhs_is_null_literal = false]'
src/foo/src/tests.cpp|20 col 3| required from here
/usr/include/gtest/gtest.h|1325 col 16| error: no match for 'operator==' (operand types are 'const pcl::PointXYZ' and 'const pcl::PointXYZ')
||    if (expected == actual) {
||                 ^
/usr/include/gtest/internal/gtest-linked_ptr.h|213 col 6| note: candidate: template<class T> bool testing::internal::operator==(T*, const testing::internal::linked_ptr<T>&)
||  bool operator==(T* ptr, const linked_ptr<T>& x) {
||       ^
/usr/include/gtest/internal/gtest-linked_ptr.h|213 col 6| note:   template argument deduction/substitution failed:
/usr/include/gtest/gtest.h|1325 col 16| note:   mismatched types 'T*' and 'pcl::PointXYZ'

我试着坚持使用这个底漆:https: //github.com/google/googletest/blob/master/googletest/docs/primer.md#binary-comparison

特别是,我的运算符在包含gtest之前定义,我确定类型匹配.我也尝试编写重载来获取const引用,但这只是比较了地址而不是值.

Answer 1

通过参数依赖查找找到自定义类型的运算符.

依赖于参数的查找(简而言之)意味着如果函数在与其一个或多个参数相同的命名空间中定义,则可以考虑这些函数.

这段代码:

namespace pcl { struct PointXYZ; }

bool operator==(pcl::PointXYZ p1, pcl::PointXYZ p2) {return p1.x-p2.x<.1;}

定义PointXYZ的pcl::命名空间,但是定义operator==在全局命名空间功能.因此,不是 ADL的候选人.

这样做:

namespace pcl { 
  struct PointXYZ; 
  bool operator==(pcl::PointXYZ p1, pcl::PointXYZ p2) {return p1.x-p2.x<.1;}
}

修复了因为现在operator ==的名称pcl::operator==与其参数之一在同一名称空间中(实际上在这种情况下都是这两个,但你明白了).这使它成为ADL期间的候选者,因此当gtest调用相等性测试时将选择它.