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type-switches.go
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type-switches.go
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/*
Type switches
A type switch is a construct that permits several type assertions in series.
A type switch is like a regular switch statement, but the cases in a type switch specify types (not values), and those values are compared against the type of the value held by the given interface value.
switch v := i.(type) {
case T:
// here v has type T
case S:
// here v has type S
default:
// no match; here v has the same type as i
}
The declaration in a type switch has the same syntax as a type assertion i.(T), but the specific type T is replaced with the keyword type.
This switch statement tests whether the interface value i holds a value of type T or S. In each of the T and S cases, the variable v will be of type T or S respectively and hold the value held by i. In the default case (where there is no match), the variable v is of the same interface type and value as i.
*/
package main
import "fmt"
func do(i interface{}) {
switch v := i.(type) {
case int:
fmt.Printf("Twice %v is %v\n", v, v*2)
case string:
fmt.Printf("%q is %v bytes long\n", v, len(v))
default:
fmt.Printf("I don't know about type %T!\n", v)
}
}
func main() {
do(21)
do("hello")
do(true)
}