Actually, that's not a band-aid. It allows strings to be generic over allocators without suffering the performance penalty of a virtual call on every malloc and free. Go's solution would be to just take the penalty of a virtual call (as interfaces require virtual calls everywhere) and try to make it up with devirtualization optimizations and/or inlining.
> After all, nobody comes into every Lisp thread demanding that Lisp grow a type-checker.
That's because making a workable type system for Lisp is a very hard problem. By contrast, generics are well known at this point.
However, compile-time polymorphism is a mixed bag because of how it tends to blow out the icache by generating many copies of similar code. Java does away with it completely, and nobody seems to be protesting. The Linux kernel is written in C, and nobody seems to be protesting that the lack of compile-time polymorphism makes his/her job impossible. Clearly, the decision as to whether to include compile-time polymorphism in a language is something reasonable people can disagree about.
With regard to a type system for Lisp: it's been done before. Check out Qi.
There is a difference in Go, and that is you don't need to explicitly implement the interface. That is, you don't need to declare that you do. But I am unconvinced that is so different from implementing interfaces in C++ and Java that C++ and Java programmers "need time and an open mind" to understand Go idioms.
Don't get me wrong: I think Go is a neat language and culture. I like many aspects of it. And I know the stance the designers of Go have on generics: they would like to do them, but they can't think of a design that they like. And they don't consider it that important, so they've bunted on it. They may do them in the future. But I find it strange when people who are not the designers of the language argue against having them, in any form.
Think about the sorting example I wrote earlier: https://news.ycombinator.com/item?id=7080562 If you were writing it in Java, is sort.Sort an interface or an abstract base class? Well, you can only "extend" one class (single inheritance only), so you would probably want Sort to be a Java interface. That means that you would always have to implement all three functions, not just one as I did, since Java interfaces cannot have default implementations. The comments indicate that most posters didn't even consider the idea that you could reuse the StringSlice functions. That method of easy composition simply doesn't exist in Java.
In general, generics get used a lot as a band-aid to avoid multiple inheritance in C++ and Java. You can't (or shouldn't, in C++) have your Foo inherit from both a (non-abstract) Bar and Baz. But you can certainly template on them. In C++, this kind of thing is called "traits" and Alexandrescu wrote a whole book about it. It's also why std::string is actually std::basic_string<char, std::char_traits<char>, std::allocator<char> >. In Go, you don't need all this... you just implement as many interfaces as you like and you're done.
So the Java and C++ programmers need time and an open mind to get up to speed. There's also another contingent of programmers that really just wants Go to be like their favorite strongly-typed functional programming language (Haskell, Scheme, SML, etc.) I like to think that these people will eventually give up. After all, nobody comes into every Lisp thread demanding that Lisp grow a type-checker. People have sort of accepted that that is not what Lisp is about and that there are other languages that will give you that if you want. Hopefully much the same will happen for Golang.