More precisely: they wanted the integer type that was large enough and ran their code fastest.

On CPUs with 64-bit and 32-bit registers, that typically is the register-sized integer type. Machines with 16-bit registers are a bit of an edge case, as 16-bit integers may both be a lot faster on them then 32-bit integers and, in many cases, too small)

If go chose to use 32-bit integers as default, some users on 64-bit systems would complain that they couldn’t create, say, an array of 6 billion ints. If they chose 64-bit, some users on 32-bit systems would complain their loops were needlessly slow, and code bloated (why waste 4 bytes of almost every integer in a program?)

Not having generics makes this more of a problem. If go had generics, switching between integer sizes could be a matter of recompilation using a different compiler flag)

A sufficiently advanced compiler would help here, but go doesn’t have one (not exceptional), and doesn’t even aim to have one (compilation speed seems more of a goal than run-time speed)

> Not having generics makes this more of a problem. If go had generics, switching between integer sizes could be a matter of recompilation using a different compiler flag)

Isn't it already the case that you can switch between int sizes with compiler flags?

    var i int

That will be 32 bits if I compile it with GOOS=linux GOARCH=386 and will be 32 bits if I swap in amd64 instead of 386 there.

Is there any language where generics are useful for switching between int sizes? None come to mind offhand, so I don't quite understand what you mean.

Traditionally the register size was too small, it's very common to have numbers above 256 or 65536. It's not true anymore with 32 bits numbers and a limit of 2 billion.