diff --git a/src/flags.rs b/src/flags.rs
index 4a263ac..61a0f4f 100644
--- a/src/flags.rs
+++ b/src/flags.rs
@@ -89,7 +89,7 @@ pub enum Flush
 impl Flush
 {
 #[inline(always)]
-    const fn get_ms(self) -> c_int
+    pub(super) const fn get_ms(self) -> c_int
     {
         use libc::{
             MS_SYNC, MS_ASYNC,
@@ -116,7 +116,7 @@ pub enum Advice {
 impl Advice
 {
 #[inline(always)]
-    const fn get_madv(self) -> c_int
+    pub(crate) const fn get_madv(self) -> c_int
     {
         use libc::{
             MADV_NORMAL,
diff --git a/src/lib.rs b/src/lib.rs
index fe864b4..68c9033 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -5,9 +5,19 @@ use libc::{
 };
 
 use std::{
+    os::unix::prelude::*,
     ops,
     mem,
-    ptr,
+    ptr::{
+	self,
+	NonNull,
+    },
+    io,
+    fmt, error,
+
+    borrow::{
+	Borrow, BorrowMut,
+    }
 };
 
 mod uniq;
@@ -40,3 +50,387 @@ pub struct MappedFile<T>
 }
 
 //TODO: continue copying from the `TODO` line in `utf8encode/src/mmap.rs`
+impl<T: AsRawFd> MappedFile<T> {
+    /// Map the file `file` to `len` bytes with memory protection as provided by `perm`, and
+    /// mapping flags provided by `flags`.
+    ///
+    /// # Returns
+    /// If `mmap()` fails, then the current `errno` is returned alongside the `file` that was passed in, otherwise, a new mapping is
+    /// constructed over `file`, and that is returned.
+    ///
+    /// # Panics
+    /// If `mmap()` succeeds, but returns an invalid address (e.g. 0)
+    pub fn try_new(file: T, len: usize, perm: Perm, flags: Flags) -> Result<Self, TryNewError<T>>
+    {
+	#[inline(never)]
+	#[cold]
+        fn _panic_invalid_address() -> !
+        {
+            panic!("Invalid/unsupported address returned from mmap()")
+        }
+	const NULL: *mut libc::c_void = ptr::null_mut();
+        let fd = file.as_raw_fd();
+        let slice = match unsafe {
+            mmap(ptr::null_mut(), len, perm.get_prot(), flags.get_flags(), fd, 0)
+        } {
+            MAP_FAILED => return Err(TryNewError::wrap_last_error(file)),
+            NULL => _panic_invalid_address(),
+            ptr => unsafe {
+                UniqueSlice {
+                    mem: NonNull::new_unchecked(ptr as *mut u8),
+                    end: match NonNull::new((ptr as *mut u8).add(len)) {
+			Some(n) => n,
+			_ => _panic_invalid_address(),
+		    },
+                }
+            },
+        };
+        Ok(Self {
+            file,
+            map: MappedSlice(slice)
+        })
+    }
+    
+    /// Map the file `file` to `len` bytes with memory protection as provided by `perm`, and
+    /// mapping flags provided by `flags`.
+    ///
+    /// # Returns
+    /// If `mmap()` fails, then the current `errno` set by `mmap()` is returned, otherwise, a new mapping is
+    /// constructed over `file`, and that is returned.
+    /// If `mmap()` fails, `file` is dropped. To retain `file`, use `try_new()`.
+    ///
+    /// # Panics
+    /// If `mmap()` succeeds, but returns an invalid address (e.g. 0)
+    #[inline] 
+    pub fn new(file: T, len: usize, perm: Perm, flags: Flags) -> io::Result<Self>
+    {
+	Self::try_new(file, len, perm, flags).map_err(Into::into)
+    }
+
+    /// Sync the mapped memory to the backing file store via `msync()`.
+    ///
+    /// If this is a private mapping, or is mapped over a private file descriptor that does not refer to on-disk persistent storage, syncing the data is usually pointless.
+    ///
+    /// # Returns
+    /// If `msync()` fails.
+    pub fn flush(&mut self, flush: Flush) -> io::Result<()>
+    {
+        use libc::msync;
+        match unsafe {
+	    msync(self.map.0.as_mut_ptr() as *mut _, self.map.0.len(), flush.get_ms())
+	} {
+            0 => Ok(()),
+            _ => Err(io::Error::last_os_error())
+        }
+    }
+
+    /// Replace the mapped file object with another that aliases the same file descriptor.
+    ///
+    /// # Warning
+    /// * The old file object is *not* dropped to prevent the file descriptor being closed. (see `replace_inner_unchecked()`).
+    ///  If `T` contains other resources, this can cause a memory leak.
+    ///
+    /// # Panics
+    /// If `other`'s `AsRawFd` impl *does not* alias the already contained `T`'s.
+    pub fn replace_inner<U: AsRawFd>(self, other: U) -> MappedFile<U>
+    {
+        assert_eq!(self.file.as_raw_fd(), other.as_raw_fd(), "File descriptors must alias");
+	unsafe {
+	    let (this, file) = self.replace_inner_unchecked(other);
+	    mem::forget(file);
+	    this
+	}
+    }
+    
+    /// Unmap the memory contained in `T` and return it.
+    /// Before the memory is unmapped, it is `msync()`'d according to `flush`.
+    ///
+    /// # Panics
+    /// If `msync()` fails.
+    #[inline]
+    pub fn into_inner_synced(mut self, flush: Flush) -> T
+    {
+        self.flush(flush).expect("Failed to sync data");
+        drop(self.map);
+        self.file
+    }
+}
+
+impl<T> MappedFile<T> {
+    
+    
+    #[inline(always)]
+    fn raw_parts(&self) -> (*mut u8, usize)
+    {
+        (self.map.0.mem.as_ptr(), self.map.0.len())
+    } 
+
+    /// Set advise according to `adv`, and optionally advise the kernel on if the memory will be needed or not.
+    pub fn advise(&mut self, adv: Advice, needed: Option<bool>) -> io::Result<()>
+    {
+        use libc::{
+            madvise,
+            MADV_WILLNEED,
+            MADV_DONTNEED
+        };
+        let (addr, len) = self.raw_parts();
+        match unsafe { madvise(addr as *mut _, len, adv.get_madv() | needed.map(|n| n.then(|| MADV_WILLNEED).unwrap_or(MADV_DONTNEED)).unwrap_or(0)) } {
+            0 => Ok(()),
+            _ => Err(io::Error::last_os_error())
+        }
+    }
+
+    /// With advice, used as a builder-pattern alternative for `advise()`.
+    ///
+    /// # Returns
+    /// If `madvise()` fails, then the `io::Error` along with the previous instance is returned.
+    #[inline(always)] 
+    pub fn try_with_advice(mut self, adv: Advice, needed: Option<bool>) -> Result<Self, TryNewError<Self>>
+    {
+        match self.advise(adv, needed) {
+            Ok(_) => Ok(self),
+	    Err(error) => Err(TryNewError {
+		error: Box::new(error),
+		value: self,
+	    })
+	}
+    }
+
+    /// With advice, used as a builder-pattern alternative for `advise()`.
+    ///
+    /// # Returns
+    /// If `madvise()` fails, then the mapping is dropped and the error is returned. To keep the previous instance if the call failes, use `try_with_advice()`.
+    #[inline] 
+    pub fn with_advice(self, adv: Advice, needed: Option<bool>) -> io::Result<Self>
+    {
+	self.try_with_advice(adv, needed).map_err(Into::into)
+    }
+    
+    /// Replace the inner file with another without checking static or dynamic bounding.
+    /// This function is extremely unsafe if the following conditions are not met in entirity.
+    ///
+    /// # Safety
+    /// * `U` and `T` **must** have an `AsRawFd::as_raw_fd()` impl that returns the same `RawFd` value unconditionally.
+    /// * The returned `T` in the tuple **must not** attempt close the file descriptor while the returned `MappedFile<U>` in the tuple is alive.
+    /// * The returned values **should not** *both* attempt to close the file descriptor when dropped. To prevent the `MappedFile<U>` from attempting to close the file descriptor, use `MappedFile::into_inner()` and ensure `U` does not close the file descriptor while `T` is alive. Alternatively, use a mechanism of `T` to prevent it from closing the file descriptor while `U` is alive.
+    #[inline(always)]
+    pub unsafe fn replace_inner_unchecked<U>(self, other: U) -> (MappedFile<U>, T)
+    {
+        let MappedFile{ file, map } = self;
+        (MappedFile {
+            file: other,
+            map
+        }, file)
+    }
+
+    /// Unmap the memory contained in `T` and return it.
+    ///
+    /// # Warning
+    /// If the map is shared, or refers to a persistent file on disk, you should call `flush()`
+    /// first or use `into_inner_synced()`
+    #[inline] 
+    pub fn into_inner(self) -> T
+    {
+        drop(self.map);
+        self.file
+    }
+
+    /// The size of the mapped memory
+    #[inline]
+    pub fn len(&self) -> usize
+    {
+        self.map.0.len()
+    }
+
+    /// Get a slice of the mapped memory
+    #[inline]
+    pub fn as_slice(&self) -> &[u8]
+    {
+        &self.map.0[..]
+    }
+
+    /// Get a mutable slice of the mapped memory
+    #[inline]
+    pub fn as_slice_mut(&mut self) -> &mut [u8]
+    {
+        &mut self.map.0[..]
+    }
+
+    /// Get a raw slice of the mapped memory
+    #[inline] 
+    pub fn as_raw_slice(&self) -> *const [u8]
+    {
+	self.map.0.as_raw_slice()
+    }
+
+    /// Get a raw mutable slice of the mapped memory
+    #[inline]
+    pub fn as_raw_slice_mut(&mut self) -> *mut [u8]
+    {
+	self.map.0.as_raw_slice_mut()
+    }
+
+    /// Checks if the mapping dangles (i.e. `len() == 0`.)
+    #[inline]
+    pub fn is_empty(&self) -> bool
+    {
+        self.map.0.is_empty()
+    }
+}
+
+/// Contains an OS error and a value.
+pub struct TryNewError<T: ?Sized>
+{
+    error: Box<io::Error>,
+    value: T
+}
+
+impl<T:?Sized> error::Error for TryNewError<T>
+{
+    #[inline] 
+    fn source(&self) -> Option<&(dyn error::Error + 'static)> {
+	Some(self.error.as_ref())
+    }
+}
+
+impl<T:?Sized> fmt::Display for TryNewError<T>
+{
+    #[inline] 
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
+    {
+	write!(f, "error in mapping of type {}", std::any::type_name::<T>())
+    }
+}
+
+impl<T:?Sized> fmt::Debug for TryNewError<T>
+{
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
+    {
+	f.debug_struct("TryNewError")
+	    .field("error", &self.error)
+	    .finish_non_exhaustive()
+    }
+}
+
+impl<T: ?Sized> TryNewError<T>
+{
+    /// A reference to the value
+    #[inline] 
+    pub fn value(&self) -> &T
+    {
+	&self.value
+    }
+    /// A mutable reference to the value
+    #[inline] 
+    pub fn value_mut(&mut self) -> &mut T
+    {
+	&mut self.value
+    }
+    /// A reference to the IO error
+    #[inline] 
+    pub fn error(&self) -> &io::Error
+    {
+	&self.error
+    }
+    /// Consume a boxed instance and return the boxed IO error.
+    #[inline] 
+    pub fn into_error_box(self: Box<Self>) -> Box<io::Error>
+    {
+	self.error
+    }
+}
+
+impl<T> TryNewError<T>
+{
+    #[inline] 
+    fn wrap_last_error(value: T) -> Self
+    {
+	Self {
+	    error: Box::new(io::Error::last_os_error()),
+	    value,
+	}
+    }
+    /// Consume into the contained value 
+    #[inline] 
+    pub fn into_inner(self) -> T
+    {
+	self.value
+    }
+
+    /// Consume into the IO error
+    #[inline] 
+    pub fn into_error(self) -> io::Error
+    {
+	*self.error
+    }
+    /// Consume into the value and the error.
+    #[inline] 
+    pub fn into_parts(self) -> (T, io::Error)
+    {
+	(self.value, *self.error)
+    }
+}
+
+impl<T: ?Sized> From<Box<TryNewError<T>>> for io::Error
+{
+    #[inline] 
+    fn from(from: Box<TryNewError<T>>) -> Self
+    {
+	*from.error
+    }
+}
+
+impl<T> From<TryNewError<T>> for io::Error
+{
+    #[inline] 
+    fn from(from: TryNewError<T>) -> Self
+    {
+	from.into_error()
+    }
+}
+
+impl<T: AsRawFd> Borrow<T> for MappedFile<T>
+{
+    #[inline]
+    fn borrow(&self) -> &T
+    {
+        &self.file
+    }
+}
+
+impl<T> Borrow<[u8]> for MappedFile<T>
+{
+    #[inline]
+    fn borrow(&self) -> &[u8]
+    {
+        self.as_slice()
+    }
+}
+
+impl<T> BorrowMut<[u8]> for MappedFile<T>
+{
+    #[inline]
+    fn borrow_mut(&mut self) -> &mut [u8]
+    {
+        self.as_slice_mut()
+    }
+}
+
+impl<T> ops::Deref for MappedFile<T>
+{
+    type Target=  [u8];
+    #[inline]
+    fn deref(&self) -> &Self::Target
+    {
+        self.as_slice()
+    }
+}
+impl<T> ops::DerefMut for MappedFile<T>
+{
+    #[inline]
+    fn deref_mut(&mut self) -> &mut Self::Target
+    {
+        self.as_slice_mut()
+    }
+}