code review 4973055: exp/sql{,/driver}: new database packages

src/pkg/exp/sql/convert.go

Index: src/pkg/exp/sql/convert.go
===================================================================
new file mode 100644
--- /dev/null
+++ b/src/pkg/exp/sql/convert.go
@@ -0,0 +1,106 @@
+// 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 (
+	"fmt"
+	"os"
+	"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{}) os.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 os.NewError("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
+}