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