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// Copyright 2015 Michal Witkowski. All Rights Reserved.
// See LICENSE for licensing terms.
package flagz
import (
flag ""
// DynFloat64 creates a `Flag` that represents `float64` which is safe to change dynamically at runtime.
func DynFloat64(flagSet *flag.FlagSet, name string, value float64, usage string) *DynFloat64Value {
dynValue := &DynFloat64Value{ptr: unsafe.Pointer(&value)}
flag := flagSet.VarPF(dynValue, name, "", usage)
return dynValue
// DynFloat64Value is a flag-related `float64` value wrapper.
type DynFloat64Value struct {
ptr unsafe.Pointer
validator func(float64) error
notifier func(oldValue float64, newValue float64)
// Get retrieves the value in a thread-safe manner.
func (d *DynFloat64Value) Get() float64 {
p := (*float64)(atomic.LoadPointer(&d.ptr))
return *p
// Set updates the value from a string representation in a thread-safe manner.
// This operation may return an error if the provided `input` doesn't parse, or the resulting value doesn't pass an
// optional validator.
// If a notifier is set on the value, it will be invoked in a separate go-routine.
func (d *DynFloat64Value) Set(input string) error {
val, err := strconv.ParseFloat(input, 64)
if err != nil {
return err
if d.validator != nil {
if err := d.validator(val); err != nil {
return err
oldPtr := atomic.SwapPointer(&d.ptr, unsafe.Pointer(&val))
if d.notifier != nil {
go d.notifier(*(*float64)(oldPtr), val)
return nil
// WithValidator adds a function that checks values before they're set.
// Any error returned by the validator will lead to the value being rejected.
// Validators are executed on the same go-routine as the call to `Set`.
func (d *DynFloat64Value) WithValidator(validator func(float64) error) *DynFloat64Value {
d.validator = validator
return d
// WithNotifier adds a function is called every time a new value is successfully set.
// Each notifier is executed in a new go-routine.
func (d *DynFloat64Value) WithNotifier(notifier func(oldValue float64, newValue float64)) *DynFloat64Value {
d.notifier = notifier
return d
// Type is an indicator of what this flag represents.
func (d *DynFloat64Value) Type() string {
return "dyn_float64"
// String returns the canonical string representation of the type.
func (d *DynFloat64Value) String() string {
return fmt.Sprintf("%v", d.Get())
// ValidateDynFloat64Range returns a validator that checks if the float value is in range.
func ValidateDynFloat64Range(fromInclusive float64, toInclusive float64) func(float64) error {
return func(value float64) error {
if value > toInclusive || value < fromInclusive {
return fmt.Errorf("value %v not in [%v, %v] range", value, fromInclusive, toInclusive)
return nil
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