394 lines
9.6 KiB
Go
394 lines
9.6 KiB
Go
// Package convert ...
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//
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// Description : 任意类型之间的相互转换
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//
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// Author : go_developer@163.com<张德满>
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//
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// Date : 2021-02-23 10:23 下午
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package convert
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/*
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Desc : 在处理一些参数的时候，可能需要将参数转换为各种类型，这里实现一个通用的转换函数，实现各种类型之间的相互转换。
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当然，如果源数据格式和目标数据类型不一致，是会返回错误的。例如将字符串“一二三”转换为数值类型则会报错，而将字符串“123”转换为数值类型则OK。
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这段代码实际抄自go自带的“database/sql”库，只是源代码作为内部函数无法在外面调用，可以单独把需要的功能拎出来使用：
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代码中有一个Scaner接口，可以自行实现，然后通过"convertAssign()"函数，作为dst参数传入。
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Author : zhangdeman001@ke.com<张德满>
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*/
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import (
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"errors"
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"fmt"
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"reflect"
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"strconv"
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"time"
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)
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// RawBytes is a byte slice that holds a reference to memory owned by
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// the database itself. After a Scan into a RawBytes, the slice is only
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// valid until the next call to Next, Scan, or Close.
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type RawBytes []byte
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var errNilPtr = errors.New("destination pointer is nil") // embedded in descriptive error
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// convertAssign copies to dest the value in src, converting it if possible.
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// An error is returned if the copy would result in loss of information.
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// dest should be a pointer type.
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func ConvertAssign(dest, src interface{}) error {
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// Common cases, without reflect.
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switch s := src.(type) {
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case string:
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switch d := dest.(type) {
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case *string:
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if d == nil {
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return errNilPtr
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}
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*d = s
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return nil
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case *[]byte:
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if d == nil {
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return errNilPtr
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}
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*d = []byte(s)
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return nil
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case *RawBytes:
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if d == nil {
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return errNilPtr
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}
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*d = append((*d)[:0], s...)
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return nil
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}
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case []byte:
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switch d := dest.(type) {
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case *string:
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if d == nil {
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return errNilPtr
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}
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*d = string(s)
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return nil
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case *interface{}:
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if d == nil {
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return errNilPtr
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}
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*d = cloneBytes(s)
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return nil
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case *[]byte:
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if d == nil {
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return errNilPtr
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}
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*d = cloneBytes(s)
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return nil
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case *RawBytes:
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if d == nil {
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return errNilPtr
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}
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*d = s
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return nil
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}
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case time.Time:
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switch d := dest.(type) {
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case *time.Time:
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*d = s
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return nil
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case *string:
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*d = s.Format(time.RFC3339Nano)
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return nil
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case *[]byte:
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if d == nil {
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return errNilPtr
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}
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*d = []byte(s.Format(time.RFC3339Nano))
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return nil
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case *RawBytes:
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if d == nil {
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return errNilPtr
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}
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*d = s.AppendFormat((*d)[:0], time.RFC3339Nano)
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return nil
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}
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case nil:
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switch d := dest.(type) {
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case *interface{}:
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if d == nil {
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return errNilPtr
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}
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*d = nil
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return nil
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case *[]byte:
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if d == nil {
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return errNilPtr
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}
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*d = nil
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return nil
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case *RawBytes:
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if d == nil {
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return errNilPtr
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}
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*d = nil
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return nil
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}
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}
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var sv reflect.Value
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switch d := dest.(type) {
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case *string:
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sv = reflect.ValueOf(src)
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switch sv.Kind() {
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case reflect.Bool,
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reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
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reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
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reflect.Float32, reflect.Float64:
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*d = asString(src)
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return nil
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}
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case *[]byte:
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sv = reflect.ValueOf(src)
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if b, ok := asBytes(nil, sv); ok {
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*d = b
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return nil
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}
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case *RawBytes:
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sv = reflect.ValueOf(src)
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if b, ok := asBytes([]byte(*d)[:0], sv); ok {
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*d = RawBytes(b)
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return nil
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}
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case *bool:
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bv, err := Bool.ConvertValue(src)
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if err == nil {
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*d = bv.(bool)
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}
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return err
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case *interface{}:
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*d = src
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return nil
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}
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if scanner, ok := dest.(Scanner); ok {
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return scanner.Scan(src)
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}
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dpv := reflect.ValueOf(dest)
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if dpv.Kind() != reflect.Ptr {
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return errors.New("destination not a pointer")
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}
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if dpv.IsNil() {
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return errNilPtr
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}
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if !sv.IsValid() {
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sv = reflect.ValueOf(src)
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}
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dv := reflect.Indirect(dpv)
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if sv.IsValid() && sv.Type().AssignableTo(dv.Type()) {
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switch b := src.(type) {
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case []byte:
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dv.Set(reflect.ValueOf(cloneBytes(b)))
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default:
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dv.Set(sv)
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}
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return nil
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}
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if dv.Kind() == sv.Kind() && sv.Type().ConvertibleTo(dv.Type()) {
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dv.Set(sv.Convert(dv.Type()))
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return nil
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}
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// The following conversions use a string value as an intermediate representation
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// to convert between various numeric types.
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//
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// This also allows scanning into user defined types such as "type Int int64".
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// For symmetry, also check for string destination types.
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switch dv.Kind() {
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case reflect.Ptr:
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if src == nil {
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dv.Set(reflect.Zero(dv.Type()))
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return nil
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}
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dv.Set(reflect.New(dv.Type().Elem()))
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return ConvertAssign(dv.Interface(), src)
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case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
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s := asString(src)
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i64, err := strconv.ParseInt(s, 10, dv.Type().Bits())
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if err != nil {
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err = strconvErr(err)
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return fmt.Errorf("converting driver.Value type %T (%q) to a %s: %v", src, s, dv.Kind(), err)
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}
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dv.SetInt(i64)
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return nil
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case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
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s := asString(src)
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u64, err := strconv.ParseUint(s, 10, dv.Type().Bits())
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if err != nil {
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err = strconvErr(err)
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return fmt.Errorf("converting driver.Value type %T (%q) to a %s: %v", src, s, dv.Kind(), err)
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}
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dv.SetUint(u64)
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return nil
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case reflect.Float32, reflect.Float64:
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s := asString(src)
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f64, err := strconv.ParseFloat(s, dv.Type().Bits())
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if err != nil {
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err = strconvErr(err)
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return fmt.Errorf("converting driver.Value type %T (%q) to a %s: %v", src, s, dv.Kind(), err)
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}
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dv.SetFloat(f64)
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return nil
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case reflect.String:
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switch v := src.(type) {
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case string:
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dv.SetString(v)
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return nil
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case []byte:
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dv.SetString(string(v))
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return nil
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}
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}
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return fmt.Errorf("unsupported Scan, storing driver.Value type %T into type %T", src, dest)
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}
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func strconvErr(err error) error {
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if ne, ok := err.(*strconv.NumError); ok {
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return ne.Err
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}
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return err
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}
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func cloneBytes(b []byte) []byte {
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if b == nil {
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return nil
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}
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c := make([]byte, len(b))
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copy(c, b)
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return c
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}
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func ToString(src interface{}) string {
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return asString(src)
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}
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func asString(src interface{}) string {
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switch v := src.(type) {
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case string:
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return v
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case []byte:
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return string(v)
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}
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rv := reflect.ValueOf(src)
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switch rv.Kind() {
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case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
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return strconv.FormatInt(rv.Int(), 10)
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case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
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return strconv.FormatUint(rv.Uint(), 10)
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case reflect.Float64:
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return strconv.FormatFloat(rv.Float(), 'g', -1, 64)
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case reflect.Float32:
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return strconv.FormatFloat(rv.Float(), 'g', -1, 32)
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case reflect.Bool:
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return strconv.FormatBool(rv.Bool())
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}
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return fmt.Sprintf("%v", src)
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}
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func asBytes(buf []byte, rv reflect.Value) (b []byte, ok bool) {
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switch rv.Kind() {
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case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
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return strconv.AppendInt(buf, rv.Int(), 10), true
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case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
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return strconv.AppendUint(buf, rv.Uint(), 10), true
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case reflect.Float32:
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return strconv.AppendFloat(buf, rv.Float(), 'g', -1, 32), true
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case reflect.Float64:
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return strconv.AppendFloat(buf, rv.Float(), 'g', -1, 64), true
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case reflect.Bool:
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return strconv.AppendBool(buf, rv.Bool()), true
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case reflect.String:
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s := rv.String()
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return append(buf, s...), true
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}
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return
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}
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// Value is a value that drivers must be able to handle.
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// It is either nil, a type handled by a database driver's NamedValueChecker
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// interface, or an instance of one of these types:
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//
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// int64
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// float64
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// bool
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// []byte
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// string
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// time.Time
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type Value interface{}
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type boolType struct{}
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var Bool boolType
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func (boolType) String() string { return "Bool" }
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func (boolType) ConvertValue(src interface{}) (Value, error) {
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switch s := src.(type) {
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case bool:
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return s, nil
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case string:
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b, err := strconv.ParseBool(s)
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if err != nil {
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return nil, fmt.Errorf("sql/driver: couldn't convert %q into type bool", s)
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}
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return b, nil
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case []byte:
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b, err := strconv.ParseBool(string(s))
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if err != nil {
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return nil, fmt.Errorf("sql/driver: couldn't convert %q into type bool", s)
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}
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return b, nil
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}
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sv := reflect.ValueOf(src)
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switch sv.Kind() {
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case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
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iv := sv.Int()
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if iv == 1 || iv == 0 {
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return iv == 1, nil
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}
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return nil, fmt.Errorf("sql/driver: couldn't convert %d into type bool", iv)
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case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
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uv := sv.Uint()
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if uv == 1 || uv == 0 {
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return uv == 1, nil
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}
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return nil, fmt.Errorf("sql/driver: couldn't convert %d into type bool", uv)
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}
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return nil, fmt.Errorf("sql/driver: couldn't convert %v (%T) into type bool", src, src)
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}
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type Scanner interface {
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// Scan assigns a value from a database driver.
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//
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// The src value will be of one of the following types:
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//
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// int64
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// float64
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// bool
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// []byte
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// string
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// time.Time
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// nil - for NULL values
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//
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// An error should be returned if the value cannot be stored
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// without loss of information.
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//
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// Reference types such as []byte are only valid until the next call to Scan
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// and should not be retained. Their underlying memory is owned by the driver.
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// If retention is necessary, copy their values before the next call to Scan.
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Scan(src interface{}) error
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}
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