如何将ErrorCode（int32）分配给原型数据的变量（* ErrorCode）

Question

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?

Answer 1

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 <kbd>play.golang.org</kbd>.