It's being switched on the type of v (string or other, in this case), though in a more complex case you could easily have several different types. The assignment basically redefines v to be the matched type inside the case statement. You could easily just add a "sv := v.(string)" as the first statement of "case string", then use sv in place of v within that block, but this does read much cleaner.

I think it gets more interesting when using several, often complex (struct) types in the same switch statement.

> It looks like v is being reassigned to the type of v,

v is not being reassigned, it is being declared (note := rather than =). But its a little complicated, because type switches are a special syntax construct that is similar to, but different than, regular expression switches. See, "Type switches" in the language reference [1]

[1] you'll have to scroll down a little within the section on Switch statements: http://golang.org/ref/spec#Switch_statements

"type" is a magic word in Go, and in that example. It's highly idiomatic -- it's inconsistent with the rest of the language (Using "type" instead of an actual type), but it makes sense once you memorize the idiom. Sort of perlish -- there are two different operations that look basically the same, and the correct one is chosen based on context (in this case, the context is "is there a type name, or "type" literally?)

Perhaps it would have been cleaner to use "*" or some other operator symbol instead of the reserved word "type"

> "type" is a magic word in Go, and in that example.

Specifically, type switches are a specific syntax construct that look very similar to normal switches, but switched on something that looks like a type assertion with "type" in place of an actual type.