MicroPosts

• Comparing any to nil in Golang

  package main
  
  import (
  	"fmt"
  )
  
  func main() {
  	var a *int = nil
  
  	var b any = nil
  	fmt.Printf("b=%T\n", b) // b=<nil>
  	b = a
  
  	fmt.Printf("a=%T\n", a) // a=*int
  	fmt.Printf("b=%T\n", b) // b=*int
  
  	fmt.Printf("b=%v\n", a == b)   // true [1]
  	fmt.Printf("b=%v\n", a == nil) // true [2]
  	fmt.Printf("b=%v\n", b == nil) // false [3]
  
  	var n *int = nil
  	fmt.Printf("b=%v\n", b == n) // true
  }
  
  // [1]: typeOf(a) == typeOf(b)   && valueOf(a) == valueOf(b)
  //      *int      == *int        && nil        == nil
  
  // [2]: typeOf(a) == typeOf(nil) && valueOf(a) == valueOf(nil)
  //      *int      == *int        && nil        == nil
  //      the compiler casts nil to *nil because it knows the type of a
  
  // [3]: typeOf(b) == typeOf(nil) && valueOf(b) == valueOf(nil)
  //      *int      == <nil>       && nil        == nil
  //      the compiler casts nil to <nil> because it knows the type of b