I am making my own programming language. I made classes (like 'string' or 'int) that derive from the object class. I am making standard types like string and int so I have a base I can work off (expand my language with itself if that makes sense). Each standard type has a unordered_map of functions. I would love to hear a way to fix this/another approach.
When I run the program, I get this error that I don't understand:
C2664: 'std::pair<const _Kty,_Ty>::pair(std::pair<const _Kty,_Ty> &&)': cannot convert argument 2 from '_Ty' to 'const _Ty2 &'
It's referring to line 62. Where the error comes from:
c:\\program files (x86)\\microsoft visual studio\\2017\\community\\vc\\tools\\msvc\\14.16.27023\\include\\xmemory0 line:881
The code from xmemory0:
template<class _Objty,
class... _Types>
static void construct(_Alloc&, _Objty * const _Ptr, _Types&&... _Args)
{ // construct _Objty(_Types...) at _Ptr
::new (const_cast<void *>(static_cast<const volatile void *>(_Ptr)))
_Objty(_STD forward<_Types>(_Args)...);
}
My code:
#include <iostream>
#include <unordered_map>
#include <string>
#include <functional>
struct Object;
typedef std::unordered_map<std::string, std::function<Object*(std::string*)>> stdtypefunc_map;
struct Object
{
};
struct StdType : public Object
{
stdtypefunc_map functions;
};
struct stringtype : public StdType
{
stringtype()
{
functions.emplace("GetValue", &stringtype::GetValue);
}
Object* GetValue(std::string args[])
{
std::cout << "GetValue()" << std::endl;
}
};
int main()
{
stringtype s;
return 0;
}
In your code, line 62 is this statement:
functions.emplace("GetValue", &stringtype::GetValue);
functions
is an std::unordered_map
whose key_type
is std::string
and mapped_type
is std::function<Object*(std::string*)>
.
emplace()
constructs a new std::unordered_map::value_type
in the map, passing the values you specify to the value_type
's constructor. In this case, that value_type
is a std::pair<const std::string, std::function<Object*(std::string*)>>
, and you are passing in 2 values to constructor the std::pair
with.
The error message you are seeing is basically saying that the compiler can't convert &stringtype::GetValue
to std::function<Object*(std::string*)>
. For example, here is a simplified example that reproduces the same failure, and GCC gives a VERY DETAILED error message explaining why it failed (which is too large to post here, so I'll post only the relevant pieces):
#include <iostream>
#include <unordered_map>
#include <string>
#include <functional>
struct Object;
typedef std::unordered_map<std::string, std::function<Object*(std::string*)>> stdtypefunc_map;
struct Object
{
};
struct StdType : public Object
{
stdtypefunc_map functions;
};
struct stringtype : public StdType
{
stringtype()
{
functions.emplace("GetValue", &stringtype::GetValue);
}
Object* GetValue(std::string args[])
{
std::cout << "GetValue()" << std::endl;
}
};
int main()
{
stringtype s;
return 0;
}
/usr/include/c++/6/ext/new_allocator.h:120:4: error: no matching function for call to ‘std::pair<const std::__cxx11::basic_string<char>, std::function<Object*(std::__cxx11::basic_string<char>*)> >::pair(const char [9], Object* (stringtype::*)(std::__cxx11::basic_string<char>*))’ { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); } ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ... /usr/include/c++/6/ext/new_allocator.h:120:4: note: cannot convert ‘std::forward<Object* (stringtype::*)(std::__cxx11::basic_string<char>*)>((* & __args#1))’ (type ‘Object* (stringtype::*)(std::__cxx11::basic_string<char>*)’) to type ‘const std::function<Object*(std::__cxx11::basic_string<char>*)>&’ { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); } ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...
Which makes sense. You can't store a pointer-to-member-method for a non-static method into a std::function
unless you take into account that it will need an object instance to call the method on. Such as by using std::bind()
to bind an object instance with the pointer-to-member-method:
using std::placeholders::_1;
functions.emplace("GetValue", std::bind(&stringtype::GetValue, this, _1));
Or, by using a lambda to capture the object:
functions.emplace("GetValue", [this](std::string *args){ return this->GetValue(args); });
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