Goでfold実装

fold.go

package main

//go:generate genny -in=$GOFILE -out=gen-$GOFILE gen "Type=string,int"

import (
	"github.com/cheekybits/genny/generic"
)

type Type generic.Type

func FoldType(l []Type, apply func(a Type, b Type) Type) (res Type) {
	res = l[0]
	for _, v := range l[1:] {
		res = apply(res, v)
	}
	return res
}

gen-fold.go

// This file was automatically generated by genny.
// Any changes will be lost if this file is regenerated.
// see https://github.com/cheekybits/genny

package main

func FoldString(l []string, apply func(a string, b string) string) (res string) {
	res = l[0]
	for _, v := range l[1:] {
		res = apply(res, v)
	}
	return res
}

func FoldInt(l []int, apply func(a int, b int) int) (res int) {
	res = l[0]
	for _, v := range l[1:] {
		res = apply(res, v)
	}
	return res
}

main.go

package main

import "fmt"

func main() {
	list := []int{1, 2, 3, 4, 5}
	res := FoldInt(list, func(a int, b int) int { return a + b })
	fmt.Printf("%[1]d(type:%[1]T)\n", res)

	slist := []string{"foo", "bar", "baz"}
	sres := FoldString(slist, func(a string, b string) string { return a + ", " + b })
	fmt.Printf("%[1]s(type:%[1]T)\n", sres)
}

ビルド

go get github.com/cheekybits/genny
go generate
go build .

出力

15(type:int)
foo, bar, baz(type:string)

この事例に限るのかもしれませんが、他の方法に比べ
非常に明瞭かつ簡潔にかけて、オーバーヘッドが少なく、コンパイル時に型チェックされ型安全です。