在Go中检查字符串指针的长度

How do I go about finding the length of a string pointer which comes from a struct. Currently I am writing unit tests and want to see whether a string pointer is less than 250 characters. If r is my and myString is a string pointer.

This code is not valid:

if len(r.myString) > 256 {
    return ErrStringTooLong
}

you can access an object with a star before pointer variable name for eg len(*r.myString)

playground example

You should explain why your code is not correct, and which error message you get. If it is a pointer to a string, you should dereference it by asterix *

len(*r.myString)