database/sql: add NullInt16 support

[kyleconroy]

Hey Go team!

I maintain a database code generator. I'm having trouble correctly supporting null smallint columns because the database/sql package does not have a NullInt16 type. It would look almost identical to Nullint32 and NullInt64.

// NullInt16 represents an int32 that may be null.
// NullInt16 implements the Scanner interface so
// it can be used as a scan destination, similar to NullString.
type NullInt16 struct {
	Int16 int16
	Valid bool // Valid is true if Int16 is not NULL
}

// Scan implements the Scanner interface.
func (n *NullInt16) Scan(value interface{}) error {
	if value == nil {
		n.Int16, n.Valid = 0, false
		return nil
	}
	n.Valid = true
	return convertAssign(&n.Int16, value)
}

// Value implements the driver Valuer interface.
func (n NullInt16) Value() (driver.Value, error) {
	if !n.Valid {
		return nil, nil
	}
	return int64(n.Int16), nil
}

[ianlancetaylor]

CC @kardianos

[kardianos]

@kyleconroy This looks reasonable. Can you send a CL?

On a side note, these nullable wrappers would probably be a great use for generics...

[kyleconroy]

Yeah, can do. A bit swamped right now, but should have it done by the end of the week

[kyleconroy]

On a side note, these nullable wrappers would probably be a great use for generics...

I know! Here's a four-line replacement for the various sql.Null* types in the standard library.

    type Null(type T) struct {
        Val   T
        Valid bool // Valid is true if Val is not NULL
    }

Here's what it looks like in practice: https://go2goplay.golang.org/p/Qj8MqYWWAc3

[rsc]

Do we need NullByte for tinyint too?
(No luck for 24-bit mediumint)

[kardianos]

NullByte and NullInt16 both sound good. Might as well complete the family.

[rsc]

Based on the discussion above, this seems like a likely accept.

[rsc]

No change in consensus, so accepted.

[muhlemmer]

I have some spare time and like to contribute more to the Go project. May I volunteer for a CL @kyleconroy, or do you prefer to do it yourself?