std: Add Option.{result_or_default,or_default} that uses Default

src/librustc/middle/typeck/check/_match.rs

@@ -173,7 +173,7 @@ pub fn check_pat_variant(pcx: &pat_ctxt, pat: @ast::Pat, path: &ast::Path,
                     fcx.write_error(pat.id);
                     kind_name = "[error]";
                     arg_types = (*subpats).clone()
-                                          .unwrap_or(~[])
+                                          .unwrap_or_default()
                                           .map(|_| ty::mk_err());
                 }
             }
@@ -222,7 +222,7 @@ pub fn check_pat_variant(pcx: &pat_ctxt, pat: @ast::Pat, path: &ast::Path,
             fcx.write_error(pat.id);
             kind_name = "[error]";
             arg_types = (*subpats).clone()
-                                  .unwrap_or(~[])
+                                  .unwrap_or_default()
                                   .map(|_| ty::mk_err());
         }
     }

src/libstd/option.rs

@@ -350,6 +350,26 @@ impl<T> Option<T> {
     }
 }
 
+impl<T: Default> Option<T> {
+    /// Returns the contained value or default (for this type)
+    #[inline]
+    pub fn unwrap_or_default(self) -> T {
+        match self {
+            Some(x) => x,
+            None => Default::default()
+        }
+    }
+
+    /// Returns self or `Some`-wrapped default value
+    #[inline]
+    pub fn or_default(self) -> Option<T> {
+        match self {
+            None => Some(Default::default()),
+            x => x,
+        }
+    }
+}
+
 impl<T> Default for Option<T> {
     fn default() -> Option<T> { None }
 }

src/libsyntax/parse/parser.rs

@@ -3461,7 +3461,7 @@ impl Parser {
         let ident = self.parse_ident();
         let opt_bounds = self.parse_optional_ty_param_bounds();
         // For typarams we don't care about the difference b/w "<T>" and "<T:>".
-        let bounds = opt_bounds.unwrap_or(opt_vec::Empty);
+        let bounds = opt_bounds.unwrap_or_default();
         ast::TyParam { ident: ident, id: ast::DUMMY_NODE_ID, bounds: bounds }
     }