func AsString(v Value) (string, error) {
	if v == nil {
		return "", fmt.Errorf(errNilConversionFormat, TypeString)
	}
	return v.asString()
}
AsString returns a string only when the type of Value is TypeString,
otherwise it returns error.
package data
import (
	"encoding/base64"
	"fmt"
	"math"
	"strconv"
	"strings"
	"time"
)
const (
	MaxConvFloat64 = float64(math.MaxInt64)
	MinConvFloat64 = float64(math.MinInt64)
	errNilConversionFormat = "cannot convert nil to %v"
)
func AsBool(v Value) (bool, error) {
	if v == nil {
		return false, fmt.Errorf(errNilConversionFormat, TypeBool)
	}
	return v.asBool()
}
func AsInt(v Value) (int64, error) {
	if v == nil {
		return 0, fmt.Errorf(errNilConversionFormat, TypeInt)
	}
	return v.asInt()
}
func AsFloat(v Value) (float64, error) {
	if v == nil {
		return 0, fmt.Errorf(errNilConversionFormat, TypeFloat)
	}
	return v.asFloat()
}