This is where confuses me the most while learning go. We all know that methods on T only affect the copy of T, and methods on *T will affect the actual data on T.
Why does methods on T can also be used by *T, but the opposite is not allowed? So,can you give me an example(or reason) on why they do not allow method on *T be used by T?
What is the pros and cons of this design?
分享 You have the key to your answer in your question: methods on T only affect the copy of T. So with this information, the following excerpt from Go's FAQ should help clear the rest of the confusion:
From the Go Spec:
"The method set of any other named type T consists of all methods with receiver type T. The method set of the corresponding pointer type *T is the set of all methods with receiver *T or T (that is, it also contains the method set of T)."
If an interface value contains a pointer *T, a method call can obtain a value by dereferencing the pointer, but if an interface value contains a value T, there is no useful way for a method call to obtain a pointer.
Even in cases where the compiler could take the address of a value to pass to the method, if the method modifies the value the changes will be lost in the caller. As a common example, this code:
var buf bytes.Buffer io.Copy(buf, os.Stdin)would copy standard input into a copy of buf, not into buf itself. This is almost never the desired behavior.
分享
