Need assistance translating this C++ template

[anonymous via Digitalmars-d-learn]

On Monday, 27 October 2014 at 22:43:23 UTC, John wrote:
> The C++ code:
>
> // Bitfield utilities
> template<unsigned bitno, unsigned nbits=1, typename T=u8>
> struct RegBit
> {
[...]
>     template<typename T2>
>     RegBit& operator=(T2 val)
[...]
> };
>
> My D implementation thus far:
[...]
> template RegBit(uint bitno, uint nbits = 1, T = u8) {

You're missing the struct here. Add some (template) parameters to
a struct, and it becomes a struct template:

struct RegBit(uint bitno, uint nbits = 1, T = u8)

[...]
>     // FIXME: Nested template frustration here... HELP
>     void opAssign(T2 val)

Similarly, add another set of (template) parameters to a
function/method, before the runtime parameters, and it becomes a
function/method template:

      void opAssign(T2)(T2 val)

[...]
> }

Those "slap another set of parameters on, and it's a template"
syntaxes, are sugar for the longer "eponymous member" variant:

struct Foo(T) {}

is equivalent to

template Foo(T)
{
      struct Foo /* same name as the template */
      {
          /* ... */
      }
}

Works with structs, classes, functions, etc.

So if you wanted to spell the templates out, it would look like
this:

template RegBit(uint bitno, uint nbits = 1, T = u8)
{
      struct RegBit
      {
          /* ... other members of RegBit ... */
          template opAssign(T2)
          {
              void opAssign(T2 val)
              {
                  /* ... implementation of opAssign ... */
              }
          }
          /* ... other members of RegBit ... */
      }
}