diff --git a/src/compiletest/errors.rs b/src/compiletest/errors.rs
index 8bfef9da805..dcb0d2ef01d 100644
--- a/src/compiletest/errors.rs
+++ b/src/compiletest/errors.rs
@@ -52,10 +52,8 @@ fn parse_expected(line_num: uint, line: ~str) -> ~[ExpectedError] {
     let start_kind = idx;
     while idx < len && line[idx] != (' ' as u8) { idx += 1u; }
 
-    // FIXME: #4318 Instead of to_ascii and to_str_ascii, could use
-    // to_ascii_consume and to_str_consume to not do a unnecessary copy.
     let kind = line.slice(start_kind, idx);
-    let kind = kind.to_ascii().to_lower().to_str_ascii();
+    let kind = kind.to_ascii().to_lower().into_str();
 
     // Extract msg:
     while idx < len && line[idx] == (' ' as u8) { idx += 1u; }
diff --git a/src/libextra/sort.rs b/src/libextra/sort.rs
index 2a456f8de3e..2de7c1ba6dc 100644
--- a/src/libextra/sort.rs
+++ b/src/libextra/sort.rs
@@ -887,12 +887,8 @@ mod tests {
         // tjc: funny that we have to use parens
         fn ile(x: &(&'static str), y: &(&'static str)) -> bool
         {
-            // FIXME: #4318 Instead of to_ascii and to_str_ascii, could use
-            // to_ascii_move and to_str_move to not do a unnecessary clone.
-            // (Actually, could just remove the to_str_* call, but needs an deriving(Ord) on
-            // Ascii)
-            let x = x.to_ascii().to_lower().to_str_ascii();
-            let y = y.to_ascii().to_lower().to_str_ascii();
+            let x = x.to_ascii().to_lower().into_str();
+            let y = y.to_ascii().to_lower().into_str();
             x <= y
         }
 
diff --git a/src/librustc/driver/driver.rs b/src/librustc/driver/driver.rs
index 47f9fcc3ca0..c57cd134e01 100644
--- a/src/librustc/driver/driver.rs
+++ b/src/librustc/driver/driver.rs
@@ -669,10 +669,8 @@ pub fn build_session_options(binary: @str,
     for level in lint_levels.iter() {
         let level_name = lint::level_to_str(*level);
 
-        // FIXME: #4318 Instead of to_ascii and to_str_ascii, could use
-        // to_ascii_move and to_str_move to not do a unnecessary copy.
         let level_short = level_name.slice_chars(0, 1);
-        let level_short = level_short.to_ascii().to_upper().to_str_ascii();
+        let level_short = level_short.to_ascii().to_upper().into_str();
         let flags = vec::append(matches.opt_strs(level_short),
                                 matches.opt_strs(level_name));
         for lint_name in flags.iter() {
diff --git a/src/libstd/ascii.rs b/src/libstd/ascii.rs
index ec2d7566177..ddf7c934a49 100644
--- a/src/libstd/ascii.rs
+++ b/src/libstd/ascii.rs
@@ -17,7 +17,7 @@ use str::OwnedStr;
 use container::Container;
 use cast;
 use iter::Iterator;
-use vec::{CopyableVector, ImmutableVector, MutableVector};
+use vec::{ImmutableVector, MutableVector};
 use to_bytes::IterBytes;
 use option::{Some, None};
 
@@ -154,10 +154,10 @@ impl AsciiCast<Ascii> for char {
 
 /// Trait for copyless casting to an ascii vector.
 pub trait OwnedAsciiCast {
-    /// Take ownership and cast to an ascii vector without trailing zero element.
+    /// Take ownership and cast to an ascii vector.
     fn into_ascii(self) -> ~[Ascii];
 
-    /// Take ownership and cast to an ascii vector without trailing zero element.
+    /// Take ownership and cast to an ascii vector.
     /// Does not perform validation checks.
     unsafe fn into_ascii_nocheck(self) -> ~[Ascii];
 }
@@ -188,10 +188,11 @@ impl OwnedAsciiCast for ~str {
     }
 }
 
-/// Trait for converting an ascii type to a string. Needed to convert `&[Ascii]` to `~str`
+/// Trait for converting an ascii type to a string. Needed to convert
+/// `&[Ascii]` to `&str`.
 pub trait AsciiStr {
     /// Convert to a string.
-    fn to_str_ascii(&self) -> ~str;
+    fn as_str_ascii<'a>(&'a self) -> &'a str;
 
     /// Convert to vector representing a lower cased ascii string.
     fn to_lower(&self) -> ~[Ascii];
@@ -199,15 +200,14 @@ pub trait AsciiStr {
     /// Convert to vector representing a upper cased ascii string.
     fn to_upper(&self) -> ~[Ascii];
 
-    /// Compares two Ascii strings ignoring case
+    /// Compares two Ascii strings ignoring case.
     fn eq_ignore_case(self, other: &[Ascii]) -> bool;
 }
 
 impl<'self> AsciiStr for &'self [Ascii] {
     #[inline]
-    fn to_str_ascii(&self) -> ~str {
-        let cpy = self.to_owned();
-        unsafe { cast::transmute(cpy) }
+    fn as_str_ascii<'a>(&'a self) -> &'a str {
+        unsafe { cast::transmute(*self) }
     }
 
     #[inline]
@@ -443,12 +443,12 @@ mod tests {
         let v = ~[40u8, 32u8, 59u8]; assert_eq!(v.to_ascii(), v2ascii!([40, 32, 59]));
         let v = ~"( ;";              assert_eq!(v.to_ascii(), v2ascii!([40, 32, 59]));
 
-        assert_eq!("abCDef&?#".to_ascii().to_lower().to_str_ascii(), ~"abcdef&?#");
-        assert_eq!("abCDef&?#".to_ascii().to_upper().to_str_ascii(), ~"ABCDEF&?#");
+        assert_eq!("abCDef&?#".to_ascii().to_lower().into_str(), ~"abcdef&?#");
+        assert_eq!("abCDef&?#".to_ascii().to_upper().into_str(), ~"ABCDEF&?#");
 
-        assert_eq!("".to_ascii().to_lower().to_str_ascii(), ~"");
-        assert_eq!("YMCA".to_ascii().to_lower().to_str_ascii(), ~"ymca");
-        assert_eq!("abcDEFxyz:.;".to_ascii().to_upper().to_str_ascii(), ~"ABCDEFXYZ:.;");
+        assert_eq!("".to_ascii().to_lower().into_str(), ~"");
+        assert_eq!("YMCA".to_ascii().to_lower().into_str(), ~"ymca");
+        assert_eq!("abcDEFxyz:.;".to_ascii().to_upper().into_str(), ~"ABCDEFXYZ:.;");
 
         assert!("aBcDeF&?#".to_ascii().eq_ignore_case("AbCdEf&?#".to_ascii()));
 
@@ -465,7 +465,10 @@ mod tests {
     }
 
     #[test]
-    fn test_ascii_to_str() { assert_eq!(v2ascii!([40, 32, 59]).to_str_ascii(), ~"( ;"); }
+    fn test_ascii_as_str() {
+        let v = v2ascii!([40, 32, 59]);
+        assert_eq!(v.as_str_ascii(), "( ;");
+    }
 
     #[test]
     fn test_ascii_into_str() {
diff --git a/src/test/bench/shootout-k-nucleotide-pipes.rs b/src/test/bench/shootout-k-nucleotide-pipes.rs
index cfc78e1615e..8ac224003b8 100644
--- a/src/test/bench/shootout-k-nucleotide-pipes.rs
+++ b/src/test/bench/shootout-k-nucleotide-pipes.rs
@@ -72,10 +72,8 @@ fn sort_and_fmt(mm: &HashMap<~[u8], uint>, total: uint) -> ~str {
        let (k,v) = (*kv).clone();
        unsafe {
            let b = str::raw::from_utf8(k);
-           // FIXME: #4318 Instead of to_ascii and to_str_ascii, could use
-           // to_ascii_move and to_str_move to not do a unnecessary copy.
            buffer.push_str(format!("{} {:0.3f}\n",
-                                   b.to_ascii().to_upper().to_str_ascii(), v));
+                                   b.into_ascii().to_upper().into_str(), v));
        }
    }
 
@@ -84,9 +82,7 @@ fn sort_and_fmt(mm: &HashMap<~[u8], uint>, total: uint) -> ~str {
 
 // given a map, search for the frequency of a pattern
 fn find(mm: &HashMap<~[u8], uint>, key: ~str) -> uint {
-   // FIXME: #4318 Instead of to_ascii and to_str_ascii, could use
-   // to_ascii_move and to_str_move to not do a unnecessary copy.
-   let key = key.to_ascii().to_lower().to_str_ascii();
+   let key = key.into_ascii().to_lower().into_str();
    match mm.find_equiv(&key.as_bytes()) {
       option::None      => { return 0u; }
       option::Some(&num) => { return num; }