You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: mmap_windows.go
    path of file: ./repos/rclone/lib/mmap
    
    the code of the file until where you have to start completion: // Package mmap implements a large block memory allocator using
// anonymous memory maps.

//go:build windows
// +build windows

package mmap

import (
	"fmt"
	"reflect"
	"unsafe"

	"golang.org/x/sys/windows"
)

// Alloc allocates size bytes and returns a slice containing them.  If
// the allocation fails it will
    
func Alloc(size int) ([]byte, error) {
	p, err := windows.VirtualAlloc(0, uintptr(size), windows.MEM_COMMIT, windows.PAGE_READWRITE)
	if err != nil {
		return nil, fmt.Errorf("mmap: failed to allocate memory for buffer: %w", err)
	}
	var mem []byte
	sh := (*reflect.SliceHeader)(unsafe.Pointer(&mem))
	sh.Data = p
	sh.Len = size
	sh.Cap = size
	return mem, nil
}