Learn template by math vector class

[Hasan Aljudy]

Darren (dgrant at kerberos-productions dot com) wrote:
> I am learning about D template details by implementing a static sized vector
> class.  Opinions on this code (like how to solve the obvious errors) or
> alternatives that would be better practice in D would be appreciated:
> 
> class vector( T, size_t size )
> {
> private:
> T p[ size ];
> 
> public:
> this()
> {
> }
> 
> this( T[] q )
> in
> {
> assert( q.length > 0 );
> }
> body
> {
> foreach ( size_t i, T v; q )
> {
> p[ i ] = v;
> }
> }
> 
> T opIndex( size_t i ) 
> in
> {
> assert( i >= 0 && i < size );
> }
> body
> {
> return p[ i ]; 
> }
> 
> T opIndexassign( T v, size_t i ) 
> in
> {
> assert( i >= 0 && i < size );
> }
> body
> {
> p[ i ] = v;
> return p[ i ]; 
> }
> 
> T x() { return p[ 0 ]; }
> T y() { return p[ 1 ]; }
> T z() { return p[ 2 ]; }
> T w() { return p[ 3 ]; }
> 
> void x( T v ) { p[ 0 ] = v; }
> void y( T v ) { p[ 1 ] = v; }
> void z( T v ) { p[ 2 ] = v; }
> void w( T v ) { p[ 3 ] = v; }
> }
> 
> 
> example:
> vector!( float, 2 ) 2d_vector;
> 
> So the obvious problem is that upon instantiation in the example, z and w
> attributes implicitly generate array bounds errors.  Is there a form of generic
> specification in D that can be applied to solve this?
> 
> 

I think you can use static if:

static if( size < 3 ) //no z component
{
     pragma( msg, "2d vectors don't have a z component" ); //tell 
compiler to print this msg
     static assert(false); //halt compiler
}