如何声明我想要一个 const 函数引用(在模板参数中)?例如,
template< bool (&func)(int arg) >
void foo(int stuff);
但是常量?
更具体地说,如果我尝试编译以下内容icpc
:
template<bool (&func)(int arg)>
bool id(int arg) {
return func(arg);
}
class Foo {
public:
Foo() {};
virtual ~Foo() {};
bool bar(int arg) { return true; }
bool bar2(int arg) {
return id<bar>(arg);
};
};
int main() {
return 0;
}
我明白了
$ icpc foo.cpp
foo.cpp(12): error: no instance of function template "id" matches the argument list
argument types are: (int)
return id<bar>(arg);
^
compilation aborted for foo.cpp (code 2)
或者,g++
我得到
$ g++ foo.cpp
foo.cpp: In member function ‘bool Foo::bar2(int)’:
foo.cpp:13:23: error: no matching function for call to ‘id(int&)’
return id<bar>(arg);
^
foo.cpp:13:23: note: candidate is:
foo.cpp:2:6: note: template<bool (& func)(int)> bool id(int)
bool id(int arg) {
^
foo.cpp:2:6: note: template argument deduction/substitution failed:
foo.cpp:13:23: error: could not convert template argument ‘Foo::bar’ to ‘bool (&)(int)’
return id<bar>(arg);
^
但是,如果我将 bar 移到顶层,如
template<bool (&func)(int arg)>
bool id(int arg) {
return func(arg);
}
bool bar(int arg) { return true; }
class Foo {
public:
Foo() {};
virtual ~Foo() {};
bool bar2(int arg) {
return id<bar>(arg);
};
};
int main() {
return 0;
}
它编译得很好。为什么会发生这种情况,如何在不将 bar 设为全局的情况下修复它?
注意:在我的原始代码中,我收到“(非 const-qualified)无法使用类型值初始化”错误:(使用icpc
)
CollisionWorld.cpp(73): error: a reference of type "bool (&)(const Line &, vec_dimension={double}, vec_dimension={double}, vec_dimension={double}, vec_dimension={double})" (not const-qualified) cannot be initialized with a value of type "bool (const Line &, vec_dimension={double}, vec_dimension={double}, vec_dimension={double}, vec_dimension={double})"
QuadTree<Line, vec_dimension, line_inside_box_with_time> *quad_tree =
^
(与g++
)
CollisionWorld.cpp:73:58: error: could not convert template argument ‘CollisionWorld::line_inside_box_with_time’ to ‘bool (&)(const Line&, double, double, double, double)’
QuadTree<Line, vec_dimension, line_inside_box_with_time> *quad_tree =
^