encoding: add AppendText and AppendBinary #62384
Description
The MarshalText and MarshalBinary methods are a trash factory.
They create a short-lived string that is almost always garbage collectable shortly after creation.
Furthermore, the caller almost always copied the result into another buffer, resulting in further waste.
I propose the addition of the following interfaces to the "encoding" package:
// TextAppender is the interface implemented by an object
// that can append the textual representation of itself.
// If a type implements both [TextAppender] and [TextMarshaler],
// then v.MarshalText() must be semantically identical to v.AppendText(nil).
type TextAppender interface {
// AppendText appends the textual representation of itself to the end of b
// (allocating a larger slice if necessary) and returns the updated slice.
//
// Implementations must not retain b, nor mutate any bytes within b[:len(b)].
AppendText(b []byte) ([]byte, error)
}
type BinaryAppender interface {
AppendBinary([]byte) ([]byte, error)
}In addition to the above, we would update all types in the stdlib that implement MarshalText or MarshalBinary to have the Append equivalent (and switch the Marshal implementation to just call the Append variant). Also, we would teach all stdlib libraries that looks for TextMarshaler or BinaryMarshaler to also look for the append (and unmarshal) variant.