Why Does `nil([]int)` Equal `nil`, But `nil(interface{})` Doesn\'t?

Nil Slice vs. Nil Interface

In Go, a nil slice is not the same as a nil interface. This behavior is demonstrated in the following code:

<code class="go">package main

import "fmt"

func main() {
    var i []int = nil
    yes(i) // output: true
    no(i)  // output: false
}

func yes(thing []int) {
    fmt.Println(thing == nil)
}

func no(thing interface{}) {
    fmt.Println(thing == nil)
}</code>

The difference in output between the two functions is due to the way Go handles interface types.

Interface Types

An interface type in Go is a collection of methods that can be implemented by a specific value type. When an interface{} variable is used, it can hold any value of any type that implements the interface.

Nil Interface

When an interface{} variable is assigned to nil, the data field of the interface is set to nil, but the type field is not. As a result, a nil interface is not equal to nil.

Nil Slice

On the other hand, a nil slice is simply a slice with no elements. When you compare a nil slice to nil, the comparison evaluates to true because both the data and type fields of the slice are set to nil.

Conclusion

Therefore, the difference in output between the two functions in the code example is due to the fact that nil([]int) is a nil slice, while nil(interface{}) is a nil interface. A nil slice evaluates to true when compared to nil, while a nil interface evaluates to false.

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