issue creating a type in "meta-like" programming

[pholotic]

Hello all,

I've been trying to play around with structs, templates, typedefs, and all that other fun stuff that ties into the so called metaprogramming form of writing code.

What I am trying to do is create a type that has 1 typename placeholder and 7 integer placeholders. I would like to create a few constant variables of this type to serve the purpose of a standard for the rest of my code, and also intialize variables that are subject to change. My code does not compile for obvious reasons. I know there is a lot wrong, and I am unsure how to fix some of it.

.h file

namespace siu {
	class unit_def;
}

class siu::unit_def {
	const int v_max;
	const int SImax;

	// SI base units
	typedef int _dim[7]; // SImax
	/* base dim */
	static const _dim meter;
	static const _dim gram;
	static const _dim second;
	static const _dim ampere;
	static const _dim kelvin;
	static const _dim mole;
	static const _dim candela;

	template<class T, int u1, int u2, int u3, 
			  int u4, int u5, int u6, int u7> // v_max
	typedef T dim<T,u1,u2,u3,u4,u5,u6,u7>;
	/* types */ //  Ty,  m,  g,  s,  A,  K, mol, cd
	dim meter   = { int, 1,  0,  0,  0,  0,  0,  0 }; // Obviously wrong
public:
	unit_def(): SImax(7) v_max(8);
};

.cpp file

#include "units.h"

using namespace siu;

unit_def::unit_def(): SImax(7) v_max(8) 
	// Error: "siu::unit_def::unit_def()" 
	//         provides no initializer for:
{					
	/* base type */		//  m,  g,  s,  A,  K, mol, cd
	const _dim meter	= { 1,  0,  0,  0,  0,  0,  0 };
	const _dim gram		= { 0,  1,  0,  0,  0,  0,  0 };
	const _dim second	= { 0,  0,  1,  0,  0,  0,  0 };
	const _dim ampere	= { 0,  0,  0,  1,  0,  0,  0 };
	const _dim kelvin	= { 0,  0,  0,  0,  1,  0,  0 };
	const _dim mole		= { 0,  0,  0,  0,  0,  1,  0 };
	const _dim candela	= { 0,  0,  0,  0,  0,  0,  1 };
}

Thanks in advance for all help with my issue. Please, feel free to share any ideas that may make this easier/more understandable. I'm almost certain that my attempt is by no means a very good way of going about doing this. However, I've been told otherwise before.

[Cubbi]

You may be interested in boost.Units: http://www.boost.org/doc/libs/release/doc/html/boost_units.html in case you need this for practical reasons (and even for self-education, it's good to compare ideas to what's used in the existing solutions)

[pholotic]

Thanks Cubbi. I've actually already been all over the boost.Units solution. I am trying to do something similar, but I don't exactly need to specialize as much as what the boost offers. In addition, I feel like writing out my own library would help me to learn quite a bit, and I would also be aware of exactly what I have and how I did it.