[cjslep]

I don't have the hard numbers to back up the cost question, but I believe one contributing factor to the claims appearing "naive/disingenuous" to you may stem from the fact that you may be looking at the language Go from a totally different perspective than the creators when they first envisioned the language (I could be very wrong in this regard):

"Go was designed to address the problems faced in software development at Google, which led to a language that is not a breakthrough research language but is nonetheless an excellent tool for engineering large software projects"[0]

They go on to list some concrete points on the type of problems they are trying to solve:

   - slow builds
   - uncontrolled dependencies
   - each programmer using a different subset of the language
   - poor program understanding (code hard to read, poorly documented, and so on)
   - duplication of effort
   - cost of updates
   - version skew
   - difficulty of writing automatic tools
   - cross-language builds

So while I can see generics helping their goal of, say "duplication of effort", I can also see it negatively impacting bullets "different subsets of the language" and maybe "poor programming understanding" since debugging generics can be extra-painful.

I might not agree with the way they value generics but to me, it does seem reasonable given their design vision and goals.

[0] https://talks.golang.org/2012/splash.article

[spion]

With the right implementation debugging generics wont be hard. It doesn't have to be C++'s version of generics.

And I'm not buying the poor programmer understanding argument. Generics aren't that complex, they're just parameterized types. The fact that basic language libraries such as maps and slices cannot be implemented without them speak volumes about how fundamental they are when building abstractions.

My point is that most of the backpressure against generics seems to stem from perceived added complexity to the compiler and type system, and thats all. But I'm not convinced thats a valid argument. Truth be told, I'm not a language implementer. But I know that fast compilers and runtimes that implement generics exist, so I don't find the whole discussion believable.

[burntsushi]

> But I know that fast compilers and runtimes that implement generics exist, so I don't find the whole discussion believable.

Are you arguing that an implementation of generics in a programming language is free? (Whether it be performance or implementation complexity.) Because if not, then you admit there are trade offs. If there are trade offs, then it is conceivable that some circumstances (including programmer tastes) may lead to a valuation that is different from yours.

"Performance" of the compiler is a critical goal of the Go project. Could you point out for me an industrial strength compiler that supports a type system of your liking that can match the compilation speed of the Go compiler? (I can't think of one.) Because if not, then I'll have to invoke this: talk is cheap, show me the code.

[tomp]

> Are you arguing that an implementation of generics in a programming language is free? (Whether it be performance or implementation complexity.)

I am.

Performance: if you replace all generics with interface{}, you get performance that is at better or equal to current Go code.

Implementation complexity: You could add some constraints to generics, for example only interface types can be used as generic parameters, and all uses of variables/methods/functions with generic types need to have generic parameters given. In that case, there's no complexity for code that doesn't use generics. Also, generics could actually be implemented as a preprocessor that would simply insert appropriate casts from/to interface{} at calls to generic methods. Since all variables/functions in Go are declared and have known types, you could of course go further and eliminate most generic parameter annotations.

[burntsushi]

> Performance: if you replace all generics with interface{}, you get performance that is at better or equal to current Go code.

That is incorrect. Using `interface{}` incurs a significant performance penalty at runtime because you end up boxing everything. For example, you cannot cast a `[]interface{}` to an arbitrary `[]A`.

In other words, no, `interface{}` is not `void*`, sorry. If it was, Go would not be memory safe. (See golang.org for their definition of memory safety. It is strictly superior to a language like C, but e.g., less than a language like Rust.)

[tomp]

What I meant is, "better or equal to current Go code using the current version of polymorphism (which is `interface {}`)".

AFAIK it's not possible to write generic Go code without `interface {}` (or, alternatively, duplicating the code for each type).

[burntsushi]

Yes, but the tradeoff Go takes right now is "slow programmers," or "no generics." You are trading that in for "slow programs." This directly implies that generics have some sort of cost structure and are not free.

`interface{}` is very rarely used for writing "generic" code precisely because of its lack of type safety and performance implications. If you came up with a way to make it type safe without addressing performance, you've just implemented a generics scheme that will cause programs to be slower than they would be without generics (because people would start using them!).

[gnuvince]

D's dmd supports templates and is faster than gc.

[burntsushi]

Is there any evidence for this claim? After a quick Google session, the best I could find was a forum thread 4 years ago claiming that `dmd` was faster than `gc`. Is that still true today?

[f2f]

Not anymore. You're two years out of date