The Go Programming Language

12.1 Why Reflection?

Sometimes we need to write a function capable of dealing uniformly with values of types that don’t satisfy a common interface, don’t have a known representation, or don’t exist at the time we design the function—or even all three.

A familiar example is the formatting logic within fmt.Fprintf, which can usefully print an arbitrary value of any type, even a user-defined one. Let’s try to implement a function like it using what we know already. For simplicity, our function will accept one argument and will return the result as a string like fmt.Sprint does, so we’ll call it Sprint.

We start with a type switch that tests whether the argument defines a String method, and call it if so. We then add switch cases that test ...