Quote:Original post by Atm97fin
Doesn't this produce the same results with less trouble?

No it doesn't have look at the code closely, its a constant static/class member so only one instance of the member is created per class, the compiler can easily optimize the code.

where as your example creates three non-constant references per object/instance aswell as the array.

The link that Fruny gave to the older thread that gave me the idea for that, someone checked out the code generated by VS and posted there results check it out.

AFAIK anonymous unions are standard C++.

The following should be valid across conforming compilers:

class Foo
{
union
{
//......
};
};


There is a non-standard extension I used on the code I presented:

class Foo
{
union
{
struct {}; // nameless nested struct is a MS extension
};
};

i tell what would be even more impressive if someone could figure out a way to either use this technique or combined approach with unions maybe so you could return a reference to either column vector or row vector from a matrix (not nessecarilly by overloading sub-script operator) without making copies of either one and it might lead to a quick tranpose operation?

Quote:Original post by Fruny
Ok, fine. But your class is still bigger, and is not a POD-type. [wink]

You really want a vector and/or matrix class that's a POD type? You didn't design RenderWare did you?

VectorDotProduct (VectorAdd (myVec, VectorSub (myVec2, myVec3)), myVec4); // ugh!

Edit: Ok you can overload operatators on POD types anyway I'm sure, but really this solves a problem that doesn't exist with a solution that's incomprehensible. Try slipping that past your boss and see if it comes back to bite you.

Quote:Original post by bobstevens
but really this solves a problem that doesn't exist

Or the problem isn't apparent to you, indeed it is very subtle and i should have probably explained at the beginning but it does solve a problem, actually it solves two problems.

1. if you use the union method using standard compliant c++ code you'll end up with something like this:



from that code notice this part of the code:

matrix4<int> m;m[0][0] = 10;std::cout << "m[0][0]: "  <<  m[0][0] << '\n';std::cout << "m[0].g.x: " <<  m[0].g.x  << '\n';std::cout << "m.i.g.x: "  <<  m.i.g.x   << '\n';

VS using pointer to data member version:

matrix4<int> m;m[0][0] = 10;std::cout << "m[0][0]: " << m[0][0] << '\n';std::cout << "m[0].x: " << m[0].x << '\n';std::cout << "m.i.x: " << m.i.x << '\n';

which one looks more natural to work with?

2. Fine fair enough so just say for a minute you started with the union method later on you decide that you wont to make some constructors in you main vector type using constructor initializer lists using the non-array members i.e. vec x, y, z, w, the only way you can do this is by giving the internal structure vec a constructor aswell but this also isn't standard compliant code because union members are not suppose to have constructors & destructors.

pointer to data members are not hacks, its completely legitimate standard compilant code & is probably safer than using public unions.

Quote:Original post by bobstevens
that's incomprehensible.

you can easily make the "incomprehensible" part private not the case with unions so much [smile]

[Edited by - snk_kid on August 29, 2004 9:52:21 AM]

Hi first, I am very sorry to wake a old thread but I am trying to implement this trick but slightly different and I can't make it work.

In the class of snk_kid, he has a static array and x,y,z,w members, what I what is to do the opposite. i want to make the x, y, z, w static member pointer and a member array to old the data.

Id it possible I can't mannage to make it work.

[source lang='cpp']
template<typename ValueType, CoreFoundation::size_t Rows, CoreFoundation::size_t Cols>
class Vector4
{
public:
inline Vector4(ValueType x, ValueType y, ValueType z, ValueType w)
:x_(x), y_(y), z_(z), w_(w)
{

}

inline ValueType operator()(CoreFoundation::size_t index)
{
return data_[index];
};

inline const ValueType& operator()(CoreFoundation::size_t index) const
{
return data_[index];
};

private:
ValueType data_[Rows*Cols];
public:
typedef ValueType Vector4< ValueType >::* const VectorElement;

static VectorElement x_;


};

template<typename ValueType>
typename Vector4<ValueType>::VectorElement Vector4<ValueType>::x_ = &(Vector4<ValueType>::data_[0]);
[/source]


What doesn't work is the assignation of the static memeber.

anybody have a clue how to do this?

Thanks