There are my codes:
file1.go:
type ErrorCode Int32
var result ErrorCode
file2.pb.go:
type CollectionGC struct {
Result *ErrorCode `protobuf:"varint,1,opt,name=result,enum=api.ErrorCode" json:"result,omitempty"`
XXX_unrecognized []byte `json:"-"`
}
messageGC := &CollectionGC {
Result: result, // a error occurs
}
That gives:
Invalid assignment from result(ErrorCode) to Result(*ErrorCode), and fun CollectionGC.SetResult(value int32) is nonexisted in file2.pb.go.
How to avoid this error?
As a first test, if Result(*ErrorCode) expects a pointer as its argument, you could at least give it one:
Result: &result
^
- pointer to result
As this "Golang - Asterisk and Ampersand Cheatsheet" (Joseph Spurrier) summarizes:
p := Person{"Hillary", 28} stores the value
p := &Person{"Hillary", 28} stores the pointer address (reference)
PrintPerson(p) passes either the value or pointer address (reference)
PrintPerson(*p) passes the value
PrintPerson(&p) passes the pointer address (reference)
Also "Pointers in Go. Short tale of asterisk and ampersand." from piotrzurek:
& in front of variable name is used to retrieve the address of where this variable’s value is stored. That address is what the pointer is going to store.
* in front of a type name, means that the declared variable will store an address of another variable of that type (not a value of that type).
* in front of a variable of pointer type is used to retrieve a value stored at given address. In Go speak this is called dereferencing.
See play.golang.org.