无法理解一些Go代码

Question

While I was reading the code of package "net", I found some code like this:

// first returns the first address which satisfies strategy, or if
// none do, then the first address of any kind.
func (addrs addrList) first(strategy func(Addr) bool) Addr {
    for _, addr := range addrs {
        if strategy(addr) {
            return addr
        }
    }
    return addrs[0]
}

I am really confused about why the func first includes another func named func(Addr), and how does this code implement the behaviour which the comments say?

Answer 1

1 func (addrs addrList) first(strategy func(Addr) bool) Addr {
2    for _, addr := range addrs {
3        if strategy(addr) {
4            return addr
         }
     }
5    return addrs[0]
  }

In words:

1. function on addrs named first returns Addr takes strategy argument which must be a function that takes Addr and return bool.
2. for each addr in range of addrs apply function strategy on addr
3. if it (the strategy func) returns true
4. then whole function first returns that addr
5. whole function first return the very first [0] Addr from addrs, implied: which only happens if none of strategy calls on addr in range of addrs returned true.