stringer

Overview ¶

The stringer plugin generates a String method for each message.

It is enabled by the following extensions:

• stringer
• stringer_all

The stringer 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.goproto_stringer_all) = false;
  option (gogoproto.stringer_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 stringer stringer, will generate the following code:

  func (this *A) String() string {
	if this == nil {
		return "nil"
	}
	s := strings.Join([]string{`&A{`,
		`Description:` + fmt.Sprintf("%v", this.Description) + `,`,
		`Number:` + fmt.Sprintf("%v", this.Number) + `,`,
		`Id:` + fmt.Sprintf("%v", this.Id) + `,`,
		`XXX_unrecognized:` + fmt.Sprintf("%v", this.XXX_unrecognized) + `,`,
		`}`,
	}, "")
	return s
  }

and the following test code:

func TestAStringer(t *testing4.T) {
	popr := math_rand4.New(math_rand4.NewSource(time4.Now().UnixNano()))
	p := NewPopulatedA(popr, false)
	s1 := p.String()
	s2 := fmt1.Sprintf("%v", p)
	if s1 != s2 {
		t.Fatalf("String want %v got %v", s1, s2)
	}
}

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