Blitz Library Strange Initialization

[binarybob0001]

I have been trying to figure out how the Blitz numeric library was able to get commas to initialize Vectors and Matrices. For example,

TinyMatrix<double, 2, 2> m;
m = 1, 2, 3, 4;

is perfectly valid. I have looked through the source, but I don't see any operator,(T_numtype n) in there. What did he do?

[binarybob0001]

I figured it out! What it does is in the operator= overload for TinyMatrix it returns an object that has operator,(T_numtype) overloaded. That object takes as an argument an iterator to TinyMatrix. The operator, simply increments the iterator each time a new number is encountered, pretty sneaky. I made an ultra simple example utilizing the same trick (without iterators) if anyone here is curious.

class ListInit
{
 int* parr;
public:
 ListInit() { parr = NULL; }
 ListInit(int* parrz) { parr = parrz; }
 ListInit& operator,(int num) {
  *parr = num;
  parr++;
  return *this;
 }
};

class Array
{
 int arr[3];
public:
 Array() 
 {
  arr[0] = 0;
  arr[1] = 0;
  arr[2] = 0;
 }
 
 Array(int x1, int x2, int x3) 
 {
  arr[0] = x1;
  arr[1] = x2;
  arr[2] = x3;
 }
 
 ListInit operator=(int x) 
 {
  arr[0] = x;
  return ListInit(&arr[1]);
 }
 
 void Print() 
 {
  cout << arr[0] << ", " << arr[1] << ", " << arr[2] << endl;
 }
};

int main(int argc, char *argv[])
{
 Array x;
 x = 1, 2, 3;
 x.Print();
 return EXIT_SUCCESS;
}

Boost has a library completely dedicated to this kind of assignment. It is called "assign." It seems pretty interesting. Thanks for at least looking.

[Mitsukai]

thats interesting... wuld be good for sizing multidimensionals.
but there is this design issue here what would be best to use?
maybe Array.Size = 1, 2, 3; or Array.Size = [1][2][3]; (if it wuld be possible) or Array.Size[1][2][3] or ()'s

[SuperKoko]

Something like Array.SetSize[1][2][3] should be possible.

[Mitsukai]

yes but at design what would be better? Array.Size = 1, 2, 3; or Array.Size[1][2][3];