Re: Specialization of generics

[tmoran@acm.org]

>the generic is instantiated in a different way if the generic formal
>parameters match some condition?
  For example?
You could of course include a boolean constant as a parameter and
then have an "if" select which of two code sequences to run.

>One application I could think of
>would be for an image package to handle 1-bit images in a compact way.
  You might want to use tagged types.  For instance, in Claw.Bitmaps there's:

    type Basic_DIBitmap_Type is abstract new Root_DIBitmap_Type with ...

then various actual types of bitmaps are, eg,

    type Mono_DIBitmap_Type (Height, Byte_Width : Claw.Int) is
        new Basic_DIBitmap_Type (Height, Byte_Width) with record ...

    type VGA_DIBitmap_Type (Height, Width : Claw.Int) is
        new Basic_DIBitmap_Type (Height, Width) with record ...

and then the various routines whose implementation is specific to the
color depth are defined, eg,

    function Get_Size (Bitmap: in Mono_DIBitmap_Type) return Claw.Size_Type;
        -- Return the size in pixel counts of the bitmap.

    function Get_Size (Bitmap: in VGA_DIBitmap_Type) return Claw.Size_Type;
        -- Return the size in pixel counts of the bitmap.
etc.