Which is faster

result.sh

$ go test -bench .
goos: darwin
goarch: arm64
pkg: example.com/m
BenchmarkMiddleware-10           6388045               189.8 ns/op
BenchmarkList-10                 5904484               205.4 ns/op
PASS
ok      example.com/m   2.830s

zerolog_hook_test.go

package main

import (
	"io"
	"testing"

	"github.com/rs/zerolog"
)

type hookFunc func(e *zerolog.Event)

type hook1 struct {
	fn hookFunc
}

func (h *hook1) Run(e *zerolog.Event, level zerolog.Level, msg string) {
	h.fn(e)
}

func (h *hook1) add(fn func(hookFunc) hookFunc) {
	h.fn = fn(h.fn)
}

func newHook1() *hook1 {
	h := &hook1{fn: func(e *zerolog.Event) { e.Str("foo0", "bar") }}
	h.add(func(fn hookFunc) hookFunc {
		return func(e *zerolog.Event) {
			e.Str("foo1", "bar")
			fn(e)
		}
	})
	h.add(func(fn hookFunc) hookFunc {
		return func(e *zerolog.Event) {
			e.Str("foo2", "bar")
			fn(e)
		}
	})
	h.add(func(fn hookFunc) hookFunc {
		return func(e *zerolog.Event) {
			e.Str("foo3", "bar")
			fn(e)
		}
	})
	h.add(func(fn hookFunc) hookFunc {
		return func(e *zerolog.Event) {
			e.Str("foo4", "bar")
			fn(e)
		}
	})
	h.add(func(fn hookFunc) hookFunc {
		return func(e *zerolog.Event) {
			e.Str("foo5", "bar")
			fn(e)
		}
	})
	h.add(func(fn hookFunc) hookFunc {
		return func(e *zerolog.Event) {
			e.Str("foo6", "bar")
			fn(e)
		}
	})
	h.add(func(fn hookFunc) hookFunc {
		return func(e *zerolog.Event) {
			e.Str("foo7", "bar")
			fn(e)
		}
	})
	h.add(func(fn hookFunc) hookFunc {
		return func(e *zerolog.Event) {
			e.Str("foo8", "bar")
			fn(e)
		}
	})
	h.add(func(fn hookFunc) hookFunc {
		return func(e *zerolog.Event) {
			e.Str("foo9", "bar")
			fn(e)
		}
	})
	return h
}

type hook2 struct {
	fn []func(e *zerolog.Event)
}

func (h hook2) Run(e *zerolog.Event, level zerolog.Level, msg string) {
	for _, fn := range h.fn {
		fn(e)
	}
}

func newHook2() *hook2 {
	return &hook2{fn: []func(e *zerolog.Event){
		func(e *zerolog.Event) { e.Str("foo0", "bar") },
		func(e *zerolog.Event) { e.Str("foo1", "bar") },
		func(e *zerolog.Event) { e.Str("foo2", "bar") },
		func(e *zerolog.Event) { e.Str("foo3", "bar") },
		func(e *zerolog.Event) { e.Str("foo4", "bar") },
		func(e *zerolog.Event) { e.Str("foo5", "bar") },
		func(e *zerolog.Event) { e.Str("foo6", "bar") },
		func(e *zerolog.Event) { e.Str("foo7", "bar") },
		func(e *zerolog.Event) { e.Str("foo8", "bar") },
		func(e *zerolog.Event) { e.Str("foo9", "bar") },
	}}
}

func useHook1(n int) {
	logger := zerolog.New(io.Discard).Hook(newHook1())
	for i := 0; i < n; i++ {
		logger.Info().Msg("hello")
	}
}

func useHook2(n int) {
	logger := zerolog.New(io.Discard).Hook(newHook2())
	for i := 0; i < n; i++ {
		logger.Info().Msg("hello")
	}
}

func BenchmarkMiddleware(b *testing.B) {
	useHook1(b.N)
}

func BenchmarkList(b *testing.B) {
	useHook2(b.N)
}