math strategy example

mathstr.go

package main

import "fmt"

// strategy: square, factorial, absolute
// input : integer
// output : integer

type MathStrategy interface {
	assert(strategyType string) bool
	execute(input int) int
}

type SquareMathStrategy struct{}

func (s *SquareMathStrategy) assert(strategyType string) bool {
	return strategyType == "square"
}
func (s *SquareMathStrategy) execute(input int) int {
	return input * input
}

type FactorialMathStrategy struct{}

func (s *FactorialMathStrategy) assert(strategyType string) bool {
	return strategyType == "factorial"
}
func (s *FactorialMathStrategy) execute(input int) int {
	var result = input
	for i := input - 1; i > 0; i-- {
		result = result * i
	}
	return result
}

type calculator struct {
	strategyList []MathStrategy
}

func (c *calculator) cal(input int, strategyType string) int {
	for _, st := range c.strategyList {
		if st.assert(strategyType) {
			return st.execute(input)
		}
	}
	panic("unknown strategy " + strategyType)
}

var defaultCalculator = &calculator{
	strategyList: []MathStrategy{
		&SquareMathStrategy{},
		&FactorialMathStrategy{},
	},
}

func main() {
	var result = defaultCalculator.cal(4, "square")
	fmt.Println(result)

	result = defaultCalculator.cal(4, "factorial")
	fmt.Println(result)
}