gostring

Overview ¶

The gostring plugin generates a GoString method for each message. The GoString method is called whenever you use a fmt.Printf as such:

fmt.Printf("%#v", mymessage)

or whenever you actually call GoString() The output produced by the GoString method can be copied from the output into code and used to set a variable. It is totally valid Go Code and is populated exactly as the struct that was printed out.

It is enabled by the following extensions:

• gostring
• gostring_all

The gostring plugin also generates a test given it is enabled using one of the following extensions:

• testgen
• testgen_all

Let us look at:

github.com/gogo/protobuf/test/example/example.proto

Btw all the output can be seen at:

github.com/gogo/protobuf/test/example/*

The following message:

  option (gogoproto.gostring_all) = true;

  message A {
	optional string Description = 1 [(gogoproto.nullable) = false];
	optional int64 Number = 2 [(gogoproto.nullable) = false];
	optional bytes Id = 3 [(gogoproto.customtype) = "github.com/gogo/protobuf/test/custom.Uuid", (gogoproto.nullable) = false];
  }

given to the gostring plugin, will generate the following code:

  func (this *A) GoString() string {
	if this == nil {
		return "nil"
	}
	s := strings1.Join([]string{`&test.A{` + `Description:` + fmt1.Sprintf("%#v", this.Description), `Number:` + fmt1.Sprintf("%#v", this.Number), `Id:` + fmt1.Sprintf("%#v", this.Id), `XXX_unrecognized:` + fmt1.Sprintf("%#v", this.XXX_unrecognized) + `}`}, ", ")
	return s
  }

and the following test code:

func TestAGoString(t *testing6.T) {
	popr := math_rand6.New(math_rand6.NewSource(time6.Now().UnixNano()))
	p := NewPopulatedA(popr, false)
	s1 := p.GoString()
	s2 := fmt2.Sprintf("%#v", p)
	if s1 != s2 {
		t.Fatalf("GoString want %v got %v", s1, s2)
	}
	_, err := go_parser.ParseExpr(s1)
	if err != nil {
		panic(err)
	}
}

Typically fmt.Printf("%#v") will stop to print when it reaches a pointer and not print their values, while the generated GoString method will always print all values, recursively.