src/pkg/exp/sql/convert.go

// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Type conversions for Scan.

package sql

import (
	"errors"
	"fmt"
	"reflect"
	"strconv"
)

// convertAssign copies to dest the value in src, converting it if possible.
// An error is returned if the copy would result in loss of information.
// dest should be a pointer type.
func convertAssign(dest, src interface{}) error {
	// Common cases, without reflect.  Fall through.
	switch s := src.(type) {
	case string:
		switch d := dest.(type) {
		case *string:
			*d = s
			return nil
		}
	case []byte:
		switch d := dest.(type) {
		case *string:
			*d = string(s)
			return nil
		case *[]byte:
			*d = s
			return nil
		}
	}

	sv := reflect.ValueOf(src)

	switch d := dest.(type) {
	case *string:
		switch sv.Kind() {
		case reflect.Bool,
			reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
			reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
			reflect.Float32, reflect.Float64:
			*d = fmt.Sprintf("%v", src)
			return nil
		}
	}

	if scanner, ok := dest.(ScannerInto); ok {
		return scanner.ScanInto(src)
	}

	dpv := reflect.ValueOf(dest)
	if dpv.Kind() != reflect.Ptr {
		return errors.New("destination not a pointer")
	}

	dv := reflect.Indirect(dpv)
	if dv.Kind() == sv.Kind() {
		dv.Set(sv)
		return nil
	}

	switch dv.Kind() {
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		if s, ok := asString(src); ok {
			i64, err := strconv.Atoi64(s)
			if err != nil {
				return fmt.Errorf("converting string %q to a %s: %v", s, dv.Kind(), err)
			}
			if dv.OverflowInt(i64) {
				return fmt.Errorf("string %q overflows %s", s, dv.Kind())
			}
			dv.SetInt(i64)
			return nil
		}
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
		if s, ok := asString(src); ok {
			u64, err := strconv.Atoui64(s)
			if err != nil {
				return fmt.Errorf("converting string %q to a %s: %v", s, dv.Kind(), err)
			}
			if dv.OverflowUint(u64) {
				return fmt.Errorf("string %q overflows %s", s, dv.Kind())
			}
			dv.SetUint(u64)
			return nil
		}
	}

	return fmt.Errorf("unsupported driver -> Scan pair: %T -> %T", src, dest)
}

func asString(src interface{}) (s string, ok bool) {
	switch v := src.(type) {
	case string:
		return v, true
	case []byte:
		return string(v), true
	}
	return "", false
}