Avoid metadata bloat by using trait FixedSizeArray

Author: petrochenkov

src/libcore/array.rs

@@ -23,10 +23,34 @@ use marker::{Copy, Sized};
 use option::Option;
 use slice::{Iter, IterMut, SliceExt};
 
+/// Utility trait implemented only on arrays of fixed size
+///
+/// This trait can be used to implement other traits on fixed-size arrays
+/// without causing much metadata bloat.
+#[unstable(feature = "core")]
+pub trait FixedSizeArray<T> {
+    /// Converts the array to immutable slice
+    fn as_slice(&self) -> &[T];
+    /// Converts the array to mutable slice
+    fn as_mut_slice(&mut self) -> &mut [T];
+}
+
 // macro for implementing n-ary tuple functions and operations
 macro_rules! array_impls {
     ($($N:expr)+) => {
         $(
+            #[unstable(feature = "core")]
+            impl<T> FixedSizeArray<T> for [T; $N] {
+                #[inline]
+                fn as_slice(&self) -> &[T] {
+                    &self[..]
+                }
+                #[inline]
+                fn as_mut_slice(&mut self) -> &mut [T] {
+                    &mut self[..]
+                }
+            }
+
             #[stable(feature = "rust1", since = "1.0.0")]
             impl<T:Copy> Clone for [T; $N] {
                 fn clone(&self) -> [T; $N] {

src/libcore/lib.rs

@@ -129,6 +129,7 @@ pub mod default;
 /* Core types and methods on primitives */
 
 pub mod any;
+pub mod array;
 pub mod atomic;
 pub mod cell;
 pub mod char;
@@ -151,7 +152,6 @@ mod bool {
 
 // note: does not need to be public
 mod tuple;
-mod array;
 
 #[doc(hidden)]
 mod core {

src/libstd/ffi/c_str.rs

@@ -11,6 +11,7 @@
 #![unstable(feature = "std_misc")]
 
 use cmp::{PartialEq, Eq, PartialOrd, Ord, Ordering};
+use core::array::FixedSizeArray;
 use error::{Error, FromError};
 use fmt;
 use io;
@@ -450,22 +451,8 @@ impl IntoBytes for String {
 impl IntoBytes for Vec<u8> {
     fn into_bytes(self) -> Vec<u8> { self }
 }
-
-macro_rules! array_impls {
-    ($($N: expr)+) => {
-        $(
-            impl<'a> IntoBytes for &'a [u8; $N] {
-                fn into_bytes(self) -> Vec<u8> { self.to_vec() }
-            }
-        )+
-    }
-}
-
-array_impls! {
-     0  1  2  3  4  5  6  7  8  9
-    10 11 12 13 14 15 16 17 18 19
-    20 21 22 23 24 25 26 27 28 29
-    30 31 32
+impl<'a, T: FixedSizeArray<u8>> IntoBytes for &'a T {
+    fn into_bytes(self) -> Vec<u8> { self.as_slice().to_vec() }
 }
 
 #[cfg(test)]

src/libstd/io/cursor.rs

@@ -11,6 +11,7 @@
 use prelude::v1::*;
 use io::prelude::*;
 
+use core::array::FixedSizeArray;
 use cmp;
 use io::{self, SeekFrom, Error, ErrorKind};
 use iter::repeat;
@@ -72,7 +73,7 @@ macro_rules! seek {
         fn seek(&mut self, style: SeekFrom) -> io::Result<u64> {
             let pos = match style {
                 SeekFrom::Start(n) => { self.pos = n; return Ok(n) }
-                SeekFrom::End(n) => self.inner.len() as i64 + n,
+                SeekFrom::End(n) => self.inner.as_slice().len() as i64 + n,
                 SeekFrom::Current(n) => self.pos as i64 + n,
             };
 
@@ -94,6 +95,7 @@ impl<'a> io::Seek for Cursor<&'a [u8]> { seek!(); }
 impl<'a> io::Seek for Cursor<&'a mut [u8]> { seek!(); }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl io::Seek for Cursor<Vec<u8>> { seek!(); }
+impl<'a, T: FixedSizeArray<u8>> io::Seek for Cursor<&'a T> { seek!(); }
 
 macro_rules! read {
     () => {
@@ -111,12 +113,13 @@ impl<'a> Read for Cursor<&'a [u8]> { read!(); }
 impl<'a> Read for Cursor<&'a mut [u8]> { read!(); }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl Read for Cursor<Vec<u8>> { read!(); }
+impl<'a, T: FixedSizeArray<u8>> Read for Cursor<&'a T> { read!(); }
 
 macro_rules! buffer {
     () => {
         fn fill_buf(&mut self) -> io::Result<&[u8]> {
-            let amt = cmp::min(self.pos, self.inner.len() as u64);
-            Ok(&self.inner[(amt as usize)..])
+            let amt = cmp::min(self.pos, self.inner.as_slice().len() as u64);
+            Ok(&self.inner.as_slice()[(amt as usize)..])
         }
         fn consume(&mut self, amt: usize) { self.pos += amt as u64; }
     }
@@ -128,23 +131,7 @@ impl<'a> BufRead for Cursor<&'a [u8]> { buffer!(); }
 impl<'a> BufRead for Cursor<&'a mut [u8]> { buffer!(); }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> BufRead for Cursor<Vec<u8>> { buffer!(); }
-
-macro_rules! array_impls {
-    ($($N: expr)+) => {
-        $(
-            impl<'a> io::Seek for Cursor<&'a [u8; $N]> { seek!(); }
-            impl<'a> Read for Cursor<&'a [u8; $N]> { read!(); }
-            impl<'a> BufRead for Cursor<&'a [u8; $N]> { buffer!(); }
-        )+
-    }
-}
-
-array_impls! {
-     0  1  2  3  4  5  6  7  8  9
-    10 11 12 13 14 15 16 17 18 19
-    20 21 22 23 24 25 26 27 28 29
-    30 31 32
-}
+impl<'a, T: FixedSizeArray<u8>> BufRead for Cursor<&'a T> { buffer!(); }
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> Write for Cursor<&'a mut [u8]> {

src/libstd/old_path/mod.rs

@@ -64,6 +64,7 @@
 #![allow(deprecated)] // seriously this is all deprecated
 #![allow(unused_imports)]
 
+use core::array::FixedSizeArray;
 use core::marker::Sized;
 use ffi::CString;
 use clone::Clone;
@@ -895,26 +896,13 @@ impl BytesContainer for [u8] {
     }
 }
 
-macro_rules! array_impls {
-    ($($N: expr)+) => {
-        $(
-            impl BytesContainer for [u8; $N] {
-                #[inline]
-                fn container_as_bytes(&self) -> &[u8] {
-                    &self[..]
-                }
-            }
-        )+
+impl<T: FixedSizeArray<u8>> BytesContainer for T {
+    #[inline]
+    fn container_as_bytes(&self) -> &[u8] {
+        self.as_slice()
     }
 }
 
-array_impls! {
-     0  1  2  3  4  5  6  7  8  9
-    10 11 12 13 14 15 16 17 18 19
-    20 21 22 23 24 25 26 27 28 29
-    30 31 32
-}
-
 impl BytesContainer for Vec<u8> {
     #[inline]
     fn container_as_bytes(&self) -> &[u8] {