pointers-and-errors.md: fmt.Printf before and after implementing String() on Balance

[mkielar]

I'm pretty new to Go, so I may not be able to explain it right, but I've noticed this:

At some point in pointers-and-errors.md, you suggest to add some fmt.Printfs to observe that the addresses are different due to the fact that the wallet object is being copied. The calls look like this:

fmt.Printf("address of balance in Deposit is %v \n", &w.balance)

and they print something like this:

address of balance in Deposit is 0xc00000a640 

I'm assuming this 0xc00000a640 is printed as Hex, because using &wallet.balance returns a pointer and that pointer is printed (when using %v) as Hex. I'm not sure (with my knowledge at this point) how Go knows it's a pointer (is there a type for pointers?) Anyway, so far so good.

However, later in the same doc, you suggest to implement a String() string method on the Balance type. Once I did that, the output of that fmt.Printf() changed to:

address of balance in Deposit is 0 BTC 

Looks like, fmt.Printf() understands that &wallet.balance is now a pointer to an instance of Stringer interface, and uses the String() method to print the value of that pointer, instead of its address.

Two issues with that:

1. That fact has been left without explanation in pointers-and-errors.md
2. I tried to have both, the Hex output and the String() method, but the best I could do, is by replacing %v with %d in the fmt.Printf() call. But then I'm no longer getting the Hex output. How can I get the "natural" behaviour of fmt.Printf when passing a pointer to it, while also having a String() string implemented on the type?

[mkielar]

Uhh, okay, I found #158, and the link to playground explains to use %p for explicitly formatting pointers, which worked. I still believe, however, that a word of explanation in the doc would be a good idea. Or maybe just use %p from the beginning and explain why?

[mkielar]

Huh, there's even a pull request for it: #616