== Quote from Ali Çehreli (acehr...@yahoo.com)'s article
> On 03/02/2011 08:56 PM, Peter Lundgren wrote:
> > Where can I go to learn about parameterized structs? I can't seem to find
> > any
> > literature on the subject. In particular, what are you allowed to use as a
> > parameter? I would like to define a struct like so:
> >
> > struct MyStruct(T, T[] a) {
> > ...
> > }
> >
> > but I receive the following error:
> >
> > Error: arithmetic/string type expected for value-parameter, not T[]
> >
> > Are arrays not allowed?
> Are you trying to parametrize by the type of the container or just
> trying to use an array of a specified type? (As opposed to say, a linked
> list of the specified type?)
> If the former, it's simple. And the simplest thing is to just use an
> array in the implementation:
> struct S(T)
> {
> T[] a;
> void foo(T element)
> {
> /* Just use like an array */
> a ~= element;
> a[0] = element;
> }
> }
> void main()
> {
> auto s = S!double();
> s.foo(1.5);
> }
> If you want to use a different container of the specified T, then a
> second template parameter can be used. This one uses an array as the
> default one:
> class SomeContainer
> {}
> struct S(T, Cont = T[])
> {
> Cont a;
> void foo(T element)
> {
> /* This time the use must match the allowed container types */
> }
> }
> void main()
> {
> auto s = S!(double, SomeContainer)();
> s.foo(1.5);
> }
> I would recommend pulling information out ;) of this page:
> http://digitalmars.com/d/2.0/template.html
> "Template Alias Parameters" is very different after C++ and can be very
> powerful:
> http://digitalmars.com/d/2.0/template.html#TemplateAliasParameter
> Ali
I'm using this for an alternative implementation of a string, if you will.
Where T
is the type of a single character and a would be the alphabet (an array of
allowed
characters). The rest of the implementation of the struct would, of course,
depend
upon the provided alphabet.
I guess value parameters can't be arbitrary types. I can probably get by with
using a string for my alphabet just fine, it just seemed an arbitrary
limitation.
Why accept only arrays of characters when the code will be the same for any
type?
