Returns this as a ClosableStringSink.
If used, this method must be the first and only call to this. It
invalidates this. All further operations must be performed on the result.
Source
/**
* Returns `this` as a [ClosableStringSink].
*
* If used, this method must be the first and only call to `this`. It
* invalidates `this`. All further operations must be performed on the result.
*/
ClosableStringSink asStringSink();