以下代码可以通过GCC 4.9.2编译,但无法通过Clang 3.5.0编译:
#include <string>
class Foo
{
public:
explicit operator std::string() const;
};
std::string bar{Foo{}}; // Works in g++, fails in clang++
std::string baz(Foo{}); // Works in both
clang++说:
foo.cpp:9:13: error: no matching constructor for initialization of 'std::string'
(aka 'basic_string<char>')
std::string bar{Foo{}};
^ ~~~~~~~
...: note: candidate constructor not viable: no known conversion from 'Foo' to
'const std::basic_string<char> &' for 1st argument
basic_string(const basic_string& __str);
^
有趣的是,如果用原始类型比如int
代替std::string
,它就能正常工作。