The key concept in "parametric polymorphism", which is what programming language nerds mean by generics, is "parametricity" [1]. This is basically the idea that all calls to a generic function should act in the same way regardless of the type of the actual concrete calls. The very first example breaks parametricity, as it multiplies for float, adds for i32, and isn't defined for other types.

It's implementation has the same issues as generics in Zig, which is also not parametric.

It's ok to explore other points in the design space, but the language designer should be aware of what they're doing and the tradeoffs involved. In the case of adhoc (non-parametric) polymorphism, there is a lot of work on type classes to draw on.

[1]: https://en.wikipedia.org/wiki/Parametricity

I don’t see how that Wikipedia page supports your claim “The key concept in "parametric polymorphism", which is what programming language nerds mean by generics, is "parametricity"”. That page doesn’t even contain the character sequence “generic”.

IMO, https://en.wikipedia.org/wiki/Generic_programming is more appropriate. It talks of “data types to-be-specified-later”, something that this and C generic lack. That’s one of the reasons that I wrote “I _somewhat_ disagree”.

Also, I don’t see how one would define “act in the same way”. A function that fully acts in the same way regardless of the types of its arguments cannot do much with its arguments.

For example, a function “/” doesn’t act in exactly the same way on floats and integers in many languages (5.0/2.0 may return 2,5 while 5/2 returns 2; if you say it should return 2,5 instead you’re having a function from T×T to T for floats but a function from T×T to U for ints; why would you call that “act in the same way”?), “+” may or may not wrap around depending on actual type, etc.