How to determine an interface{} value's "real" type?

Question

I have not found a good resource for using interface{} types. For example

package main

import "fmt"

func weirdFunc(i int) interface{} {
    if i == 0 {
        return "zero"
    }
    return i
}
func main() {
    var i = 5
    var w = weirdFunc(5)

    // this example works!
    if tmp, ok := w.(int); ok {
        i += tmp
    }

    fmt.Println("i =", i)
}

Do you know of a good introduction to using Go's interface{}?

specific questions:

• how do I get the "real" Type of w?
• is there any way to get the string representation of a type?
• is there any way to use the string representation of a type to convert a value?

Answer 1

You also can do type switches:

switch v := myInterface.(type) {
case int:
    // v is an int here, so e.g. v + 1 is possible.
    fmt.Printf("Integer: %v", v)
case float64:
    // v is a float64 here, so e.g. v + 1.0 is possible.
    fmt.Printf("Float64: %v", v)
case string:
    // v is a string here, so e.g. v + " Yeah!" is possible.
    fmt.Printf("String: %v", v)
default:
    // And here I'm feeling dumb. ;)
    fmt.Printf("I don't know, ask stackoverflow.")
}