In that example y is a nil interface value of type l. The last line implies that for a type assertion to another interface type, the operation will only be possible if the underlying value implements both interfaces. That is, the value must have an m() method as well as all of io.reader methods or the type assertion will like the above assertion to a string type.
On Oct 13, 2016 7:48 AM, <d...@veryhaha.com> wrote: On Thursday, October 13, 2016 at 8:52:14 PM UTC+8, Jan Mercl wrote: > On Thu, Oct 13, 2016 at 2:42 PM <di...@veryhaha.com> wrote: > > > I don't understand the comment of the last line. Can someone explain it > for me? > > "r has type io.Reader" means that the type if expr.(T) is T. > > "and y must implement both I and io.Reader" > > y is either nil or it implements I, because that's how it was declared and > nothing not implementing I can be assigned to it. The dynamic type of y can > implement any number of interfaces, so it can implement both I and > io.Reader. The later is checked at run time when the type assertion > expression y.(io.Reader) is actually evaluated. > > -- > > -j > So "y must implement both I and io.Reader" means short form of "the dynamic type of y must implement both I and io.Reader"? My brain really can't accept this short form. And in that example, it gives people the impression y is nil. I really think it is a bad example. I feel that comment (and that example) is very not professional for these reason: 1. y is a value of type I, -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
