Generic Middleware Composition with Variadic Closure Decorators

package main
 
import "fmt"
 
type Handler[T any] func(T) T
type Decorator[T any] func(Handler[T]) Handler[T]
 
func Compose[T any](decorators ...Decorator[T]) Decorator[T] {
	return func(final Handler[T]) Handler[T] {
		for i := len(decorators) - 1; i >= 0; i-- {
			final = decorators[i](final)
		}
		return final
	}
}
 
func main() {
	logDec := func(next Handler[int]) Handler[int] {
		return func(val int) int {
			fmt.Println("Before execution:", val)
			res := next(val)
			fmt.Println("After execution:", res)
			return res
		}
	}
 
	doubleDec := func(next Handler[int]) Handler[int] {
		return func(val int) int { return next(val * 2) }
	}
 
	pipeline := Compose(logDec, doubleDec)(func(v int) int {
		return v + 10
	})
 
	fmt.Println("Final Output:", pipeline(5))
}