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Comment by swid | Hacker News Reader

Here's the way you can solve the first problem with generics in go, almost exactly as he described:

The trick is to define the fish tank like so:

    type fishTank struct {
      container[fish]
    }

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Thanks, yep, that works. Updated the blog piece and will improve the Quamina code a bit too.

FWIW the original works as well, but because you're using a typedef (not an alias) you have to convert from your own type to the underlying:

    func (t *fishTank) fishCount() string {
        return fmt.Sprintf("How many fishies? %d!", (*container[fish])(t).size())
    }

that's because

    type fishTank container[fish]

creates a completely new and independent type with container[fish] as the underlying implementation.

An alternative is to just alias:

    type fishTank = container[fish]

however in that case you can't define methods on fishTank, because it's literally just a shorthand for container[fish].

OK, that `(*container[fish])(t).size())` idiom is um non-obvious. Somebody needs to write a nice simple bloggy step-by-step walk through all these gyrations.

It's not really an idiom. The normal conversion expression is

   T(v)

but that doesn't work if T is a pointer type, because it's parsed as

   *(T(v))

so the types don't match. So you need

    (*T)(v)

to ensure the type part includes the pointer specifier.

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