passing 2 parameters of undefined type to a constructor (of 2 expected) - function

Question

I have a constructor where as first 2 parameteres I would like to pass:
ID3D11ShaderResourceView* as a steady downloaded texture OR
const CHAR* as a filename to downlowd this texture and assign it to a class ID3D11ShaderResourceView* member (with following release on demand), but I can not understand the way I should do it correctly. it looks this way:
class {button
public
button() {};
button(data1 (or texture or filname), data2 (or texture or filname), rest data....);
...
~button();
}
so I tried:
templates but failed, may be cause of knowledge lack, templates
define one type while I need a choice of 2. Varradic templates, or I didnt get them right but they mean undetermined amount of variables when I need to differ only 2 first.
Unions but it had conflict with class variable set - said could not match const char [amount] with const char* and unions do not work with std::string.
tried void* with typeid.name() but it always showed me "void *"
I don't want to overload constructors, becuase this will create 4+ of them barely differing one from another. Do you think boost::variant helps me in this case? Is there any smooth and effective way to build that kind of constructor? My c++ knowledge is on beginning level, sorry if its a duplicate topic, read all it suggested to me while creating it but didn't seem to find out anything closely similar, thanks:)
Update:
Applied boost::any, got next results:
class button : public frame {
public:
button() {};
button(boost::any _texture,
boost::any _hover_texture,
...
};
if (_texture.type() == typeid(ID3D11ShaderResourceView*)) texture = boost::any_cast<ID3D11ShaderResourceView*>(_texture);
if (_texture.type() == typeid(const char*))
{
if ( FAILED(D3DX11CreateShaderResourceViewFromFile(gvDevice,boost::any_cast<const char*>(_texture), NULL, NULL, &texture, NULL )) )
mboxout( "loading texture failed.", "UI texture load error", true );
};
if (_hover_texture.type() == typeid(ID3D11ShaderResourceView*)) hover_texture = boost::any_cast<ID3D11ShaderResourceView*>(_hover_texture);
if (_hover_texture.type() == typeid(const char*))
{
if ( FAILED(D3DX11CreateShaderResourceViewFromFile(gvDevice, boost::any_cast<const char*>(_hover_texture), NULL, NULL, &hover_texture, NULL )) )
mboxout( "loading texture failed.", "UI texture load error", true );
};
Is it the only possible decision because this one seems akward for me? Thanks :)

Answer 1

As always, when you have combinatoric explosion/tedious repetition, refactor your code into reusable units.
In this case, your constructor could be just
template <typename T1, typename T2>
button(T1 const& texture, T2 const& hover_texture)
: _texture(load(texture)),
_hover_texture(load(hover_texture))
{
};
And all the loading logic would be inside... you guess it the load function. A sample implementation of that:
static ID3D11ShaderResourceView* load(ID3D11ShaderResourceView* v){
return v; // just return the resources passed in
}
static ID3D11ShaderResourceView* load(char const* fname) {
ID3D11ShaderResourceView* p = NULL;
if (FAILED(D3DX11CreateShaderResourceViewFromFile(gvDevice, fname, NULL, NULL, &p, NULL)))
throw std::runtime_error(std::string("loading texture failed (") + fname + ")");
return p;
}
Note: while we were at it we separated UI from business logic. You do not want to display messageboxes from inside constructors. Ever. You just want to notify the caller of the problem and the caller decides what to do (use another resource, try a different path, retry a download, write a warning message to the log, shut down etc.)
Full Demo
Live On Coliru
#include <iostream>
#include <stdexcept>
///////////////////////////////////////////////////////
// mocking ID3D*
struct ID3D11ShaderResourceView;
enum ERROR_CODE { ERR_OK };
#define FAILED(e) (ERR_OK != (e))
static int gvDevice = 42;
ERROR_CODE D3DX11CreateShaderResourceViewFromFile(int, char const* fname, void*, void*, ID3D11ShaderResourceView**, void*) {
std::cout << "Loaded from " << fname << "\n";
return ERR_OK;
}
//
///////////////////////////////////////////////////////
struct frame{ virtual ~frame() = default; };
class button : public frame {
public:
button() {};
template <typename T1, typename T2>
button(T1 const& texture, T2 const& hover_texture)
: _texture(load(texture)),
_hover_texture(load(hover_texture))
{
};
private:
// TODO Rule-Of-Three constructor/destructorl
// SUGGEST: Rule-Of-Zero using shared pointers instead
ID3D11ShaderResourceView* _texture;
ID3D11ShaderResourceView* _hover_texture;
static ID3D11ShaderResourceView* load(ID3D11ShaderResourceView* v) { return v; }
static ID3D11ShaderResourceView* load(char const* fname) {
ID3D11ShaderResourceView* p = NULL;
if (FAILED(D3DX11CreateShaderResourceViewFromFile(gvDevice, fname, NULL, NULL, &p, NULL)))
throw std::runtime_error(std::string("loading texture failed (") + fname + ")");
return p;
}
};
#include <cassert>
int main() {
ID3D11ShaderResourceView* default_texture = NULL;
assert(!FAILED( D3DX11CreateShaderResourceViewFromFile(gvDevice, "default_texture.bin", NULL, NULL, &default_texture, NULL)));
try {
button button1("t1.bin", "hover1.bin");
button button2(default_texture, "hover2.bin");
button button3("t3.bin", default_texture);
button button4(default_texture, default_texture);
} catch(std::exception const& e) {
std::cout << "Oops: " << e.what() << "\n";
}
}
Prints:
Loaded from default_texture.bin
Loaded from t1.bin
Loaded from hover1.bin
Loaded from hover2.bin
Loaded from t3.bin
There's still a lot to be improved (see the comments, e.g.) but this is a start.