Remove File interface and rename FileImpl with File

Ref: https://rakyll.org/interface-pollution/
Interfaces can be defined by the user if and when necessary.

mmap.go

@@ -2,9 +2,7 @@ package mmap
 
 import (
 	"errors"
-	"io"
 	"os"
-	"strings"
 	"syscall"
 )
 
@@ -15,25 +13,8 @@ var (
 	ErrIndexOutOfBound = errors.New("offset out of mapped region")
 )
 
-// File provides an interface to a memory mapped file
-type File interface {
-	io.ReaderAt
-	io.WriterAt
-
-	ReadStringAt(dest *strings.Builder, offset int64) int
-	WriteStringAt(src string, offset int64) int
-	ReadUint64At(offset int64) uint64
-	WriteUint64At(num uint64, offset int64)
-
-	Lock() error
-	Unlock() error
-	Advise(advice int) error
-	Flush(flags int) error
-	Unmap() error
-}
-
-// FileImpl provides abstraction around a memory mapped file
-type FileImpl struct {
+// File provides abstraction around a memory mapped file
+type File struct {
 	data   []byte
 	length int64
 }
@@ -45,21 +26,21 @@ type FileImpl struct {
 //              then all the mapped memory is accessible
 //    case 2 => if   file size <= memory region (offset + length)
 //              then from offset to file size memory region is accessible
-func NewSharedFileMmap(f *os.File, offset int64, length int, prot int) (File, error) {
+func NewSharedFileMmap(f *os.File, offset int64, length int, prot int) (*File, error) {
 	data, err := syscall.Mmap(int(f.Fd()), offset, length, prot, syscall.MAP_SHARED)
 	if err != nil {
 		return nil, err
 	}
 
-	return &FileImpl{
+	return &File{
 		data:   data,
 		length: int64(length),
 	}, nil
 }
 
 // Unmap unmaps the memory mapped file. An error will be returned
 // if any of the functions are called on Mmap after calling Unmap
-func (m *FileImpl) Unmap() error {
+func (m *File) Unmap() error {
 	err := syscall.Munmap(m.data)
 	m.data = nil
 	return err

mmap_data.go

@@ -7,7 +7,7 @@ import (
 	"unsafe"
 )
 
-func (m *FileImpl) boundaryChecks(offset, numBytes int64) {
+func (m *File) boundaryChecks(offset, numBytes int64) {
 	if m.data == nil {
 		panic(ErrUnmappedMemory)
 	} else if offset+numBytes > m.length || offset < 0 {
@@ -23,7 +23,7 @@ func (m *FileImpl) boundaryChecks(offset, numBytes int64) {
 //   Case 2: len(dest) < (m.length - offset)
 //        => copies len(dest) bytes to dest from mapped region
 // err is always nil, hence, can be ignored
-func (m *FileImpl) ReadAt(dest []byte, offset int64) (int, error) {
+func (m *File) ReadAt(dest []byte, offset int64) (int, error) {
 	m.boundaryChecks(offset, 1)
 	return copy(dest, m.data[offset:]), nil
 }
@@ -36,15 +36,15 @@ func (m *FileImpl) ReadAt(dest []byte, offset int64) (int, error) {
 //  Case 2: len(src) < (m.length - offset)
 //      => copies len(src) bytes to the mapped region from src
 // err is always nil, hence, can be ignored
-func (m *FileImpl) WriteAt(src []byte, offset int64) (int, error) {
+func (m *File) WriteAt(src []byte, offset int64) (int, error) {
 	m.boundaryChecks(offset, 1)
 	return copy(m.data[offset:], src), nil
 }
 
 // ReadStringAt copies data to dest string builder from mapped region starting at
 // given offset until the min value of (length - offset) or (dest.Cap() - dest.Len())
 // and returns number of bytes copied to the dest slice.
-func (m *FileImpl) ReadStringAt(dest *strings.Builder, offset int64) int {
+func (m *File) ReadStringAt(dest *strings.Builder, offset int64) int {
 	m.boundaryChecks(offset, 1)
 
 	dataLength := m.length - offset
@@ -60,25 +60,25 @@ func (m *FileImpl) ReadStringAt(dest *strings.Builder, offset int64) int {
 
 // WriteStringAt copies data to mapped region from the src string starting at
 // given offset and returns number of bytes copied to the mapped region.
-func (m *FileImpl) WriteStringAt(src string, offset int64) int {
+func (m *File) WriteStringAt(src string, offset int64) int {
 	m.boundaryChecks(offset, 1)
 	return copy(m.data[offset:], src)
 }
 
 // ReadUint64At reads uint64 from offset
-func (m *FileImpl) ReadUint64At(offset int64) uint64 {
+func (m *File) ReadUint64At(offset int64) uint64 {
 	m.boundaryChecks(offset, 8)
 	return binary.LittleEndian.Uint64(m.data[offset : offset+8])
 }
 
 // WriteUint64At writes num at offset
-func (m *FileImpl) WriteUint64At(num uint64, offset int64) {
+func (m *File) WriteUint64At(num uint64, offset int64) {
 	m.boundaryChecks(offset, 8)
 	binary.LittleEndian.PutUint64(m.data[offset:offset+8], num)
 }
 
 // Flush flushes the memory mapped region to disk
-func (m *FileImpl) Flush(flags int) error {
+func (m *File) Flush(flags int) error {
 	_, _, err := syscall.Syscall(syscall.SYS_MSYNC,
 		uintptr(unsafe.Pointer(&m.data[0])), uintptr(m.length), uintptr(flags))
 	if err != 0 {

mmap_page.go

@@ -6,7 +6,7 @@ import (
 )
 
 // Advise provides hints to kernel regarding the use of memory mapped region
-func (m *FileImpl) Advise(advice int) error {
+func (m *File) Advise(advice int) error {
 	_, _, err := syscall.Syscall(syscall.SYS_MADVISE,
 		uintptr(unsafe.Pointer(&m.data[0])), uintptr(m.length), uintptr(advice))
 	if err != 0 {
@@ -17,7 +17,7 @@ func (m *FileImpl) Advise(advice int) error {
 }
 
 // Lock locks all the mapped memory to RAM, preventing the pages from swapping out
-func (m *FileImpl) Lock() error {
+func (m *File) Lock() error {
 	_, _, err := syscall.Syscall(syscall.SYS_MLOCK,
 		uintptr(unsafe.Pointer(&m.data[0])), uintptr(m.length), 0)
 	if err != 0 {
@@ -28,7 +28,7 @@ func (m *FileImpl) Lock() error {
 }
 
 // Unlock unlocks the mapped memory from RAM, enabling swapping out of RAM if required
-func (m *FileImpl) Unlock() error {
+func (m *File) Unlock() error {
 	_, _, err := syscall.Syscall(syscall.SYS_MUNLOCK,
 		uintptr(unsafe.Pointer(&m.data[0])), uintptr(m.length), 0)
 	if err != 0 {