The onlyone plugin generates code for the onlyone extension.
All fields must be nullable and only one of the fields may be set, like a union.
Two methods are generated
GetValue() interface{}
and
SetValue(v interface{}) (set bool)
These provide easier interaction with a onlyone.
The onlyone extension is not called union as this causes compile errors in the C++ generated code.
There can only be one ;)
It is enabled by the following extensions:
The onlyone plugin also generates a test given it is enabled using one of the following extensions:
Lets 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:
message U {
option (gogoproto.onlyone) = true;
optional A A = 1;
optional B B = 2;
}
given to the onlyone plugin, will generate code which looks a lot like this:
func (this *U) GetValue() interface{} {
if this.A != nil {
return this.A
}
if this.B != nil {
return this.B
}
return nil
}
func (this *U) SetValue(value interface{}) bool {
switch vt := value.(type) {
case *A:
this.A = vt
case *B:
this.B = vt
default:
return false
}
return true
}
and the following test code:
func TestUUnion(t *testing.T) {
popr := math_rand.New(math_rand.NewSource(time.Now().UnixNano()))
p := NewPopulatedU(popr)
v := p.GetValue()
msg := &U{}
if !msg.SetValue(v) {
t.Fatalf("Union: Could not set Value")
}
if !p.Equal(msg) {
t.Fatalf("%#v !Union Equal %#v", msg, p)
}
}