go temperature conversion

main.go

package main

import (
	"example/pkg/temperature"
	"fmt"
)

func main() {
	t := convert.New(0, convert.Celsius)
	fmt.Println(t.F())
}

temperature.go

package temperature

type temperatureUnit int

const (
	Kelvin temperatureUnit = iota
	Celsius
	Fahrenheit
	Rankine
)

type conversionFunc func(float64) float64

const (
	rankine float64 = 9/5
	rankineInverted float64 = 5/9
)

func rankineUp(in float64) float64 { return in * rankine }
func rankineDown(in float64) float64 { return in * rankineInverted }

var funcMap = map[temperatureUnit]map[temperatureUnit]conversionFunc{
	Kelvin: {
		Celsius:    func(in float64) float64 { return in - 273.15 },
		Fahrenheit: func(in float64) float64 { return rankineUp(in) - 459.67 },
		Rankine:    rankineUp,
	},
	Celsius: {
		Kelvin: func(in float64) float64 { return in + 273.15},
		Fahrenheit: func(in float64) float64 { return rankineUp(in) + 32 },
		Rankine: func(in float64) float64 { return rankineUp(in + 273.15) },
	},
	Fahrenheit: {
		Kelvin: func(in float64) float64 { return rankineDown(in + 459.67) },
		Celsius: func(in float64) float64 { return rankineDown(in - 32)},
		Rankine: func(in float64) float64 { return in + 459.67 },
	},
	Rankine: {
		Kelvin: rankineDown,
		Celsius: func(in float64) float64 { return rankineDown(in - 491.67) },
		Fahrenheit: func(in float64) float64 { return in - 459.67 },
	},
}

type ConvertibleTemperature struct {
	Value float64
	Unit temperatureUnit
}

func New(value float64, unit temperatureUnit) *ConvertibleTemperature {
	return &ConvertibleTemperature{
		Value: value,
		Unit:  unit,
	}
}

func (T ConvertibleTemperature) Convert(to temperatureUnit) float64 {
	return funcMap[T.Unit][to](T.Value)
}

func fromTo(from, to temperatureUnit, t ConvertibleTemperature) float64 {
	if from == to { return t.Value } else {
		return t.Convert(to)
	}
}

func (T ConvertibleTemperature) C() float64 { return fromTo(T.Unit, Celsius, T) }
func (T ConvertibleTemperature) F() float64 { return fromTo(T.Unit, Fahrenheit, T) }
func (T ConvertibleTemperature) K() float64 { return fromTo(T.Unit, Kelvin, T) }
func (T ConvertibleTemperature) R() float64 { return fromTo(T.Unit, Rankine, T) }