The point to remember is that each value of a concrete type has exactly that one concrete type, while each value of an interface type has exactly one interface type and one concrete type.
It is also important to note that there is a distinction between "assignability" and "type-assertiblity". * Bakul Shah <ba...@bitblocks.com> [180225 03:48]: > https://play.golang.org/p/IMWd3cvgfsU > > // also replicated below > > package main > > import ( > "fmt" > ) > > type ( > T1 interface{ f1()int; f2()int } > T2 interface{ f2()int; f3()int } > ) > type C int > func (c C)f1()int {return 1} > func (c C)f2()int {return 2} > func (c C)f3()int {return 3} > > func main() { > var (x1 T1; x2 T2; c C; o interface{}) > fmt.Printf("%T, %T, %T, %T\n", x1, x2, o, c) > p(x1);p(x2);p(o);p(c) > > x1 = c; x2 = c; o = c > fmt.Printf("%T, %T, %T, %T\n", x1, x2, o, c) > p(x1);p(x2);p(o);p(c) ^ x2 (type T2) is assignable to the argument of p (type interface{}), but when the assignment happens, the value loses the information that it came from a value with interface type T2. The o argument to p has interface type interface{} and concrete type C, even though it came from a value with interface type T2. > } > > func p(o interface{}) { > switch o.(type) { A type switch uses the first case that can match (i.e. type-assertibility, not assignability). For the x2 case above, o still only has interface type interface{} and concrete type C. However C is type-assertible to type T1, so the first case matches (and so do all the others, except default, but the first matching case wins). > case T1: fmt.Println("T1") > case T2: fmt.Println("T2") > case C: fmt.Println("C") > case interface{}: fmt.Println("interface{}") > default: fmt.Println("<nil>?") > } > } It is also worth emphasizing that if you changed the argument to p from interface{} to T2, the following snippet would still print "T1": func main() { var x2 T2 var c C x2 = c p(x2) } func p(o T2) { // remainder of function as above ... } ...Marvin -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
