Implement size_hint for EscapeDefault

Author: semmaz

src/libcore/char.rs

@@ -147,7 +147,6 @@ pub trait CharExt {
     fn to_digit(self, radix: u32) -> Option<u32>;
     fn escape_unicode(self) -> EscapeUnicode;
     fn escape_default(self) -> EscapeDefault;
-    fn needs_escape_default(self) -> bool;
     fn len_utf8(self) -> usize;
     fn len_utf16(self) -> usize;
     fn encode_utf8(self, dst: &mut [u8]) -> Option<usize>;
@@ -186,24 +185,13 @@ impl CharExt for char {
             '\t' => EscapeDefaultState::Backslash('t'),
             '\r' => EscapeDefaultState::Backslash('r'),
             '\n' => EscapeDefaultState::Backslash('n'),
-            '\\' => EscapeDefaultState::Backslash('\\'),
-            '\'' => EscapeDefaultState::Backslash('\''),
-            '"'  => EscapeDefaultState::Backslash('"'),
+            '\\' | '\'' | '"' => EscapeDefaultState::Backslash(self),
             '\x20' ... '\x7e' => EscapeDefaultState::Char(self),
             _ => EscapeDefaultState::Unicode(self.escape_unicode())
         };
         EscapeDefault { state: init_state }
     }
 
-    #[inline]
-    fn needs_escape_default(self) -> bool {
-        match self {
-            '\\' | '\'' | '"' => true,
-            '\x20' ... '\x7e' => false,
-            _ => true
-        }
-    }
-
     #[inline]
     fn len_utf8(self) -> usize {
         let code = self as u32;
@@ -390,4 +378,13 @@ impl Iterator for EscapeDefault {
             EscapeDefaultState::Unicode(ref mut iter) => iter.next()
         }
     }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        match self.state {
+            EscapeDefaultState::Char(_) => (1, Some(1)),
+            EscapeDefaultState::Backslash(_) => (2, Some(2)),
+            EscapeDefaultState::Unicode(_) => (0, Some(10)),
+            _ => (0, Some(0))
+        }
+    }
 }

src/libcore/fmt/mod.rs

@@ -1313,11 +1313,12 @@ impl Debug for str {
         try!(f.write_char('"'));
         let mut from = 0;
         for (i, c) in self.char_indices() {
+            let esc = c.escape_default();
             // If char needs escaping, flush backlog so far and write, else skip
-            if c.needs_escape_default() {
+            if esc.size_hint().0 != 1 {
                 try!(f.write_str(&self[from..i]));
-                for e in c.escape_default() {
-                    try!(f.write_char(e));
+                for c in esc {
+                    try!(f.write_char(c));
                 }
                 from = i + c.len_utf8();
             }