CODEWITHSUNDEEP
reflectiongo
Sergei G
Sergei G

Reputation: 1690

How can I make this reflect based GO code simpler?

I am encoding a rather complex structure using a very complicated protocol that's a mix of ASN and a variant of XDR and other encodings.

I based the implementation on xdr encoder available on github. The code is reflection based and it works, but I don't like how I implemented target type switch:

st := ve.Type().String()
    switch st {
    case "time.Time":

I think the following approach might be better, but I could not get it to work properly:

switch ve.(type) {
case time.Time:

The reason it does not work is that ve is of the same reflection type and not the target type.

The following function provides full context of the code:

func (enc *encoderState) encode(v reflect.Value) {

ve := enc.indirect(v)

st := ve.Type().String()
switch st {
case "time.Time":
    log.Println("Handling time.Time")
    t, ok := ve.Interface().(time.Time)
    if !ok {
        enc.err = errors.New("Failed to type assert to time.Time")
        return
    }
    enc.encodeTime(t)
    return
case "[]uint8":
    log.Println("Handling []uint8")
    enc.writeOctetString(ve.Bytes())
    return
default:
    log.Printf("Handling type: %v by kind: %v\n", st, ve.Kind())
}

// Handle native Go types.
switch ve.Kind() {
case reflect.Uint8: // , reflect.Int8
    enc.writeUint8(uint8(v.Uint()))
    return
case reflect.Uint16: // , reflect.Int16
    enc.writeUint16(uint16(v.Uint()))
    return
case reflect.Bool:
    enc.writeBool(ve.Bool())
    return
case reflect.Struct:
    enc.encodeStruct(ve)
    return
case reflect.Interface:
    enc.encodeInterface(ve)
    return
}

// The only unhandled types left are unsupported.  At the time of this
// writing the only remaining unsupported types that exist are
// reflect.Uintptr and reflect.UnsafePointer.
enc.err = errors.New(fmt.Sprintf("unsupported Go type '%s'", ve.Kind().String()))

}

If you know of a better example that can switch by type and kind better, please, let me know.

Thank you

UPDATE

After reading the solution I adjusted to a variation that works:

vi := ve.Interface()
switch st := vi.(type) {
case time.Time:
    enc.encodeTime(vi.(time.Time))
    return
case []uint8:
    enc.writeOctetString(vi.([]byte))
    return
default:
    log.Printf("Handling type: %v by kind: %v\n", st, ve.Kind())
}

Upvotes: 2

Views: 81

Answers (1)

Thundercat
Thundercat

Reputation: 120941

Use a type switch on the underlying value:

switch v := ve.Interface().(type) {
case time.Time:
    log.Println("Handling time.Time")
    enc.encodeTime(v)
    return
case []byte:
    log.Println("Handling []uint8")
    enc.writeOctetString(v)
    return
case byte:
    enc.writeUint8(v)
    return
// ... and more types here
default:
    log.Printf("Handling type: %v by kind: %v\n", ve.Type(), ve.Kind())
}

playground example

You can also switch on the reflect.Type instead of the string:

switch ve.Type() {
case reflect.TypeOf(time.Time{}):
    log.Println("Handling time.Time")
    ...
case reflect.TypeOf([]byte{}):
    log.Println("Handling []uint8")
    ...
case reflect.TypeOf(uint8(0)):
    ...
}

playground example

Upvotes: 4

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