Macro Templates, by example.

Posted by on July 13, 2009

Heres an example of what I call “macro templates” in PureBasic. A template encapsulates certain functionality, allowing you to dynamically generate the code in a flexible manner.

This example implements a bare-bones n-vector library using a structure and a static array:

Macro Vector_Register( _n, _type )
 
	Structure VECTOR#_n#_type
		vector._type[_n]
	EndStructure
 
	Procedure._type Vector#_n#_type#_Add( *r.VECTOR#_n#_type, *a.VECTOR#_n#_type, *b.VECTOR#_n#_type )
		Define.i i
		For i=0 To _n - 1
			*r\vector[i] = *a\vector[i] + *b\vector[i]
		Next
	EndProcedure
 
	Procedure._type Vector#_n#_type#_Subtract( *r.VECTOR#_n#_type, *a.VECTOR#_n#_type, *b.VECTOR#_n#_type )
		Define.i i
		For i=0 To _n - 1
			*r\vector[i] = *a\vector[i] - *b\vector[i]
		Next
	EndProcedure
 
	Procedure._type Vector#_n#_type#_Divide( *r.VECTOR#_n#_type, *a.VECTOR#_n#_type, *b.VECTOR#_n#_type )
		Define.i i
		For i=0 To _n - 1
			If *b\vector[i] <> 0.0 And *a\vector[i] <> 0.0
				*r\vector[i] = *a\vector[i] / *b\vector[i]
			EndIf
		Next
	EndProcedure
 
	Procedure._type Vector#_n#_type#_Multiply( *r.VECTOR#_n#_type, *a.VECTOR#_n#_type, *b.VECTOR#_n#_type )
		Define.i i
		For i=0 To _n - 1
			*r\vector[i] = *a\vector[i] * *b\vector[i]
		Next
	EndProcedure
 
	Procedure._type Vector#_n#_type#_DotProduct( *a.VECTOR#_n#_type, *b.VECTOR#_n#_type )
		Define.i i
		Define._type result
		For i=0 To _n - 1
			result + ( *a\vector[i] * *b\vector[i] )
		Next
		ProcedureReturn result
	EndProcedure
 
	Procedure._type Vector#_n#_type#_Length( *v.VECTOR#_n#_type )
		ProcedureReturn Sqr( Vector#_n#_type#_DotProduct( *v, *v ) )
	EndProcedure
 
	Procedure._type Vector#_n#_type#_Distance( *a.VECTOR#_n#_type, *b.VECTOR#_n#_type )
		Define.VECTOR#_n#_type temp
		Vector#_n#_type#_Subtract( temp, *a, *b )
		ProcedureReturn Vector#_n#_type#_Length( temp )
	EndProcedure
 
	Procedure.s Vector#_n#_type#_Debug( *v.VECTOR#_n#_type, Decimals.i=#PB_Default )
		Define.i i
		Define.s tmp = "["
		For i=0 To _n-1
			tmp + StrF( *v\vector[i], Decimals.i )
			If i <> _n-1
				tmp + ", "
			EndIf
		Next
		tmp + "]"
		Debug tmp
		ProcedureReturn tmp
	EndProcedure
 
EndMacro

It might look strange/complicated at first, but once you read it you’ll realize it’s fairly simple.

Let’s see the usage of this particular template:

Vector_Register(3, f )	; Register a float "vec3".
Define.VECTOR3f a,b,c	; Define a few vectors with the new structure.
 
a\vector[0] = 10.0
a\vector[1] = 20.0
a\vector[2] = 30.0
 
b\vector[0] = 100.0
b\vector[1] = 200.0
b\vector[2] = 300.0
 
Vector3f_Add(c, a, b)	; c = a + b
Vector3f_Debug(c)	; show each element using the debug output.
 
Debug Vector3f_DotProduct( a, b )
Debug Vector3f_Length( a )
Debug Vector3f_Distance( a, b )

Cool, huh?. And you can define any amount of elements with any basic type.

Of course we sacrificed speed for flexibility. In those cases where we have to define n-vectors, this would be an ideal solution. For everything else, I suggest a specific library, such as my vec3 macro lib.

Using this principle you can abstract almost anything, within reason. One good example is my object factory template. ¬†Ideally one would have arrays, lists, etc. Implemented in this very same way, in such case the possibilities would be endless and you’d be able to define dynamic lists/arrays inside structures, etc.

I strongly advice you to implement at least one of those templates, even if it’s just for an exercise.

Having the extra tools can’t hurt!

Cheers.

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