interface{} is nothing like void* because it's type-safe. interface{} is (type, value) i.e. it remembers the type of the value it contains.
void * is just a value.
In C a cast is unsafe because it doesn't tell you if you did something wrong.
In Go, type assertion is safe. It tells you if it succeeded and if you ignore it, it'll panic, informing you that you have tried to perform an illegal operation.
I was partially incorrect. I said "reflection" could look it up, but you can check it during the conversion as you said (from Effective Go[0]). But my original point (before the edit) still holds true. You need to convert any data stored in a common data structure implementations and you don't easily know its type. So you have to track the type of the data in that structure yourself. So if you pass around a tree, linked list, or whatever, it's not clear what the type is of the stored data by the type information.
But you are right, I'm new enough to Go to forget about the 'ok' check on the type conversion. Checking errors on any unsafe operations is really the best way to go. If you are unsure of the type of a structure you are getting, you really should be checking it.
interface{} is nothing like void* because it's type-safe. interface{} is (type, value) i.e. it remembers the type of the value it contains. void * is just a value.
Your code snippet has a bug because you didn't check the type assertion result. Here's a fixed version: http://play.golang.org/p/vlsXtEmgMs
In C a cast is unsafe because it doesn't tell you if you did something wrong.
In Go, type assertion is safe. It tells you if it succeeded and if you ignore it, it'll panic, informing you that you have tried to perform an illegal operation.
For more see: http://golang.org/ref/spec#Type_assertions