proposal: Support no indentation option in func (Subtitles) WriteToTTML

[min0625]

Background

I noticed that the WriteToTTML function always indents the output. This is not a problem in most cases, but in some cases, storage space is limited, you may not want indentation.

Proposal

I propose that:

• New method WriteToTTMLWithOptions in Subtitles.
• New type TTMLWriteOptions for WriteToTTMLWithOptions.

Define the following:

// WriteToTTMLWithOptions writes subtitles in .ttml format with options.
func (s Subtitles) WriteToTTMLWithOptions(o io.Writer, opts TTMLWriteOptions) (err error) {
    // ...

	// Marshal XML
	var e = xml.NewEncoder(o)

    // Indent
    if opts.Indent != nil {
        e.Indent("", *opts.Indent)
    } else {
        e.Indent("", "    ")
    }

    // ...
}

// TTMLWriteOptions represents TTML write options.
type TTMLWriteOptions struct {
    Indent *string // Default is 4 spaces.
}

[asticode]

Good idea! 👍

However I'd rather not have an additional WriteToTTMLWithOptions() method but instead:

• rename TTMLWriteOptions into WriteToTTMLOptions
• make Indent a string
• add a type WriteToTTMLOption func(o *WriteToTTMLOptions)
• transform WriteToTTML into WriteToTTML(o io.Writer, opts ...WriteToTTMLOption)
• at the beginning of WriteToTTML do something like

// Create write options
wo := &WriteToTTMLOptions{Indent: "    "}
for _, opt := range opts {
  opt(wo)
}

• add

func WriteToTTMLWithIndentOption(indent string) WriteToTTMLOption {
  return func(o *WriteToTTMLOptions) {
    o.Indent = indent
  }
}

and use WriteToTTML(r, WriteToTTMLWithIndentOption("")) to remove indentation

[min0625]

LGTM. I will adjust the PR later.

[min0625]

Hi @asticode,

The PR is ready for review. Thanks.