encoding/json: can add UnmarshalWithUseNumber function

[gopherbot]

by runner.mei:

func UnmarshalWithUseNumber(data []byte, v interface{}) error {
            // Check for well-formedness.
            // Avoids filling out half a data structure
            // before discovering a JSON syntax error.
            var d decodeState
========================= add next line ===============
                d.useNumber = true
            err := checkValid(data, &d.scan)
            if err != nil {
                return err
            }
        
            d.init(data)
            return d.unmarshal(v)
        }

[bradfitz]

Comment 1:

Rather than provide a patch, please describe (or given a link to a play.golang.org
program) that is broken.

[gopherbot]

Comment 2 by runner.mei:

can add UnmarshalWithUseNumber function, like this:
http://play.golang.org/p/GvJ71Ybgwv

[bradfitz]

Comment 3:

We can't provide a function for every combination of options.  I think using Decoder
here is fine.

Status changed to WorkingAsIntended.

[gopherbot]

Comment 4 by runner.mei:

If you use the decoder, then data will be copied to Decoder.buf field, will increase an
unnecessary copy.
  dec := json.NewDecoder(strings.NewReader(data))
  dec.UseNumber()
  dec.Decode(&m) // data will copy to dec.buf, it is unnecessary.
 
data length is 2m in my program.

[gopherbot]

Comment 5 by runner.mei:

also add json.NewDecoderWithBytes function.
  data, _ := ioutil.ReadAll(reader)
  dec := json.NewDecoderWithBytes(data)
  dec.UseNumber()
  dec.Decode(&m)