Problem serialising VoicePrompt structs to XML

[settermjd]

While creating Go TwiML examples for the docs, I noticed that the Prompt tag is not serialised to XML correctly. This is because the tag's for attribute is written incorrectly as for_.

For example, take the following, correct, XML:

<?xml version="1.0" encoding="UTF-8"?>
<Response>
  <Pay>
   <Prompt for="payment-card-number">
     <Say>Please enter your 16 digit Visa or Mastercard number.</Say>
   </Prompt>
  </Pay>
</Response>

For example, take the code below. We would reasonably expect it to generate the XML above:

package main

import (
	"fmt"

	"github.com/twilio/twilio-go/twiml"
)

func main() {
	twiml, _ := twiml.Voice([]twiml.Element{
		&twiml.VoicePay{
			InnerElements: []twiml.Element{
				&twiml.VoicePrompt{
					For_: "payment-card-number",
					InnerElements: []twiml.Element{
						&twiml.VoiceSay{
							Message: "Please enter your 16 digit Visa or Mastercard number.",
						},
					},
				},
			},
		},
	})

	fmt.Print(twiml)
}

Unfortunately, it won't, as you can see below:

<?xml version="1.0" encoding="UTF-8"?>
<Response>
  <Pay>
    <Prompt for_="payment-card-number">
      <Say>Please enter your 16 digit Visa or Mastercard number.</Say>
    </Prompt>
  </Pay>
</Response>

The serialisation process needs to be corrected to write the for attribute correctly.

[settermjd]

From research, this can be fixed by updating VoicePrompt's GetAttr() method as follows:

func (m VoicePrompt) GetAttr() (map[string]string, map[string]string) {
	paramsAttr := map[string]string{
		"For":                   m.For_,
		"ErrorType":             m.ErrorType,
		"CardType":              m.CardType,
		"Attempt":               m.Attempt,
		"RequireMatchingInputs": m.RequireMatchingInputs,
	}
	return m.OptionalAttributes, paramsAttr
}

By doing this, when the Prompt tag is serialised, the for attribute will be written correctly.