zlacker

>>ustad+(OP)
As a long-time Go programmer I didn't understand the comment about two types of nil because I have never experienced that issue, so I dug into it.

It turns out to be nothing but a misunderstanding of what the fmt.Println() statement is actually doing. If we use a more advanced print statement then everything becomes extremely clear:

    package main

    import (
      "fmt"
      "github.com/k0kubun/pp/v3"
    )

    type I interface{}
    type S struct{}

    func main() {
      var i I
      var s *S

      pp.Println(s, i)                        // (*main.S)(nil) nil
      fmt.Println(s == nil, i == nil, s == i) // true true false

      i = s

      pp.Println(s, i)                        // (*main.S)(nil) (*main.S)(nil)
      fmt.Println(s == nil, i == nil, s == i) // true false true
    }

The author of this post has noted a convenience feature, namely that fmt.Println() tells you the state of the thing in the interface and not the state of the interface, mistaken it as a fundamental design issue and written a screed about a language issue that literally doesn't exist.

Being charitable, I guess the author could actually be complaining that putting a nil pointer inside a nil interface is confusing. It is indeed confusing, but it doesn't mean there are "two types" of nil. Nil just means empty.

>>gnfarg+8i
The author is showing the result of s==nil and i==nil, which are checks that you would have to do almost everywhere (the so called "billion dollar mistake")

It's not about Printf. It's about how these two different kind of nil values sometimes compare equal to nil, sometimes compare equal to each other, and sometimes not

Yes there is a real internal difference between the two that you can print. But that is the point the author is making.

>>tux3+on
It's a contrived example which I have never really experienced in my own code (and at this point, I've written a lot of it) or any of my team's code.

Go had some poor design features, many of which have now been fixed, some of which can't be fixed. It's fine to warn people about those. But inventing intentionally confusing examples and then complaining about them is pretty close to strawmanning.