Remove all ToStr impls, add Show impls

This commit changes the ToStr trait to:

    impl<T: fmt::Show> ToStr for T {
        fn to_str(&self) -> ~str { format!("{}", *self) }
    }

The ToStr trait has been on the chopping block for quite awhile now, and this is
the final nail in its coffin. The trait and the corresponding method are not
being removed as part of this commit, but rather any implementations of the
`ToStr` trait are being forbidden because of the generic impl. The new way to
get the `to_str()` method to work is to implement `fmt::Show`.

Formatting into a `&mut Writer` (as `format!` does) is much more efficient than
`ToStr` when building up large strings. The `ToStr` trait forces many
intermediate allocations to be made while the `fmt::Show` trait allows
incremental buildup in the same heap allocated buffer. Additionally, the
`fmt::Show` trait is much more extensible in terms of interoperation with other
`Writer` instances and in more situations. By design the `ToStr` trait requires
at least one allocation whereas the `fmt::Show` trait does not require any
allocations.

Closes #8242
Closes #9806

1 files changed, 28 insertions, 27 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index 4e43592ec5c..7561d8cbbae 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -17,11 +17,12 @@ use opt_vec::OptVec;
 use parse::token::{InternedString, special_idents, str_to_ident};
 use parse::token;
 
+use std::fmt;
+use std::fmt::Show;
 use std::cell::RefCell;
 use collections::HashMap;
 use std::option::Option;
 use std::rc::Rc;
-use std::to_str::ToStr;
 use serialize::{Encodable, Decodable, Encoder, Decoder};
 
 /// A pointer abstraction. FIXME(eddyb) #10676 use Rc<T> in the future.
@@ -39,7 +40,7 @@ pub fn P<T: 'static>(value: T) -> P<T> {
 // table) and a SyntaxContext to track renaming and
 // macro expansion per Flatt et al., "Macros
 // That Work Together"
-#[deriving(Clone, Hash, ToStr, TotalEq, TotalOrd, Show)]
+#[deriving(Clone, Hash, TotalEq, TotalOrd, Show)]
 pub struct Ident { name: Name, ctxt: SyntaxContext }
 
 impl Ident {
@@ -182,7 +183,7 @@ pub type CrateNum = u32;
 
 pub type NodeId = u32;
 
-#[deriving(Clone, TotalEq, TotalOrd, Eq, Encodable, Decodable, Hash, ToStr, Show)]
+#[deriving(Clone, TotalEq, TotalOrd, Eq, Encodable, Decodable, Hash, Show)]
 pub struct DefId {
     krate: CrateNum,
     node: NodeId,
@@ -277,7 +278,7 @@ pub enum Def {
     DefMethod(DefId /* method */, Option<DefId> /* trait */),
 }
 
-#[deriving(Clone, Eq, Hash, Encodable, Decodable, ToStr)]
+#[deriving(Clone, Eq, Hash, Encodable, Decodable, Show)]
 pub enum DefRegion {
     DefStaticRegion,
     DefEarlyBoundRegion(/* index */ uint, /* lifetime decl */ NodeId),
@@ -398,12 +399,12 @@ pub enum Sigil {
     ManagedSigil
 }
 
-impl ToStr for Sigil {
-    fn to_str(&self) -> ~str {
+impl fmt::Show for Sigil {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
-            BorrowedSigil => ~"&",
-            OwnedSigil => ~"~",
-            ManagedSigil => ~"@"
+            BorrowedSigil => "&".fmt(f),
+            OwnedSigil => "~".fmt(f),
+            ManagedSigil => "@".fmt(f),
          }
     }
 }
@@ -768,9 +769,9 @@ pub enum IntTy {
     TyI64,
 }
 
-impl ToStr for IntTy {
-    fn to_str(&self) -> ~str {
-        ast_util::int_ty_to_str(*self)
+impl fmt::Show for IntTy {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "{}", ast_util::int_ty_to_str(*self))
     }
 }
 
@@ -783,9 +784,9 @@ pub enum UintTy {
     TyU64,
 }
 
-impl ToStr for UintTy {
-    fn to_str(&self) -> ~str {
-        ast_util::uint_ty_to_str(*self)
+impl fmt::Show for UintTy {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "{}", ast_util::uint_ty_to_str(*self))
     }
 }
 
@@ -795,9 +796,9 @@ pub enum FloatTy {
     TyF64,
 }
 
-impl ToStr for FloatTy {
-    fn to_str(&self) -> ~str {
-        ast_util::float_ty_to_str(*self)
+impl fmt::Show for FloatTy {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "{}", ast_util::float_ty_to_str(*self))
     }
 }
 
@@ -826,11 +827,11 @@ pub enum Onceness {
     Many
 }
 
-impl ToStr for Onceness {
-    fn to_str(&self) -> ~str {
+impl fmt::Show for Onceness {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
-            Once => ~"once",
-            Many => ~"many"
+            Once => "once".fmt(f),
+            Many => "many".fmt(f),
         }
     }
 }
@@ -939,12 +940,12 @@ pub enum Purity {
     ExternFn, // declared with "extern fn"
 }
 
-impl ToStr for Purity {
-    fn to_str(&self) -> ~str {
+impl fmt::Show for Purity {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
-            ImpureFn => ~"impure",
-            UnsafeFn => ~"unsafe",
-            ExternFn => ~"extern"
+            ImpureFn => "impure".fmt(f),
+            UnsafeFn => "unsafe".fmt(f),
+            ExternFn => "extern".fmt(f),
         }
     }
 }