gopl-zh.github.com/vendor/gopl.io/ch7/tempconv/tempconv.go

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2015-12-09 07:45:11 +00:00
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
// See page 180.
// Package tempconv performs Celsius and Fahrenheit temperature computations.
package tempconv
import (
"flag"
"fmt"
)
type Celsius float64
type Fahrenheit float64
func CToF(c Celsius) Fahrenheit { return Fahrenheit(c*9.0/5.0 + 32.0) }
func FToC(f Fahrenheit) Celsius { return Celsius((f - 32.0) * 5.0 / 9.0) }
func (c Celsius) String() string { return fmt.Sprintf("%g°C", c) }
/*
//!+flagvalue
package flag
// Value is the interface to the value stored in a flag.
type Value interface {
String() string
Set(string) error
}
//!-flagvalue
*/
//!+celsiusFlag
// *celsiusFlag satisfies the flag.Value interface.
type celsiusFlag struct{ Celsius }
func (f *celsiusFlag) Set(s string) error {
var unit string
var value float64
fmt.Sscanf(s, "%f%s", &value, &unit) // no error check needed
switch unit {
case "C", "°C":
f.Celsius = Celsius(value)
return nil
case "F", "°F":
f.Celsius = FToC(Fahrenheit(value))
return nil
}
return fmt.Errorf("invalid temperature %q", s)
}
//!-celsiusFlag
//!+CelsiusFlag
// CelsiusFlag defines a Celsius flag with the specified name,
// default value, and usage, and returns the address of the flag variable.
// The flag argument must have a quantity and a unit, e.g., "100C".
func CelsiusFlag(name string, value Celsius, usage string) *Celsius {
f := celsiusFlag{value}
flag.CommandLine.Var(&f, name, usage)
return &f.Celsius
}
//!-CelsiusFlag