Remove the '<->' operator from the language

Author: alexcrichton

doc/rust.md

@@ -1946,35 +1946,6 @@ fn avg(v: &[float]) -> float {
 }
 ~~~~
 
-#### Swap expressions
-
-A _swap expression_ consists of an [lvalue](#lvalues-rvalues-and-temporaries) followed by a bi-directional arrow (`<->`) and another [lvalue](#lvalues-rvalues-and-temporaries).
-
-Evaluating a swap expression causes, as a side effect, the values held in the left-hand-side and right-hand-side [lvalues](#lvalues-rvalues-and-temporaries) to be exchanged indivisibly.
-
-Evaluating a swap expression neither changes reference counts,
-nor deeply copies any owned structure pointed to by the moved [rvalue](#lvalues-rvalues-and-temporaries).
-Instead, the swap expression represents an indivisible *exchange of ownership*,
-between the right-hand-side and the left-hand-side of the expression.
-No allocation or destruction is entailed.
-
-An example of three different swap expressions:
-
-~~~~~~~~
-# let mut x = &mut [0];
-# let mut a = &mut [0];
-# let i = 0;
-# struct S1 { z: int };
-# struct S2 { c: int };
-# let mut y = S1{z: 0};
-# let mut b = S2{c: 0};
-
-x <-> a;
-x[i] <-> a[i];
-y.z <-> b.c;
-~~~~~~~~
-
-
 #### Assignment expressions
 
 An _assignment expression_ consists of an [lvalue](#lvalues-rvalues-and-temporaries) expression followed by an
@@ -2015,7 +1986,7 @@ as
 == !=
 &&
 ||
-= <->
+=
 ~~~~
 
 Operators at the same precedence level are evaluated left-to-right.

src/librustc/middle/borrowck/check_loans.rs

@@ -758,10 +758,6 @@ fn check_loans_in_expr<'a>(expr: @ast::expr,
     }
 
     match expr.node {
-      ast::expr_swap(l, r) => {
-        self.check_assignment(l);
-        self.check_assignment(r);
-      }
       ast::expr_assign(dest, _) |
       ast::expr_assign_op(_, dest, _) => {
         self.check_assignment(dest);

src/librustc/middle/dataflow.rs

@@ -698,11 +698,6 @@ impl<'self, O:DataFlowOperator> PropagationContext<'self, O> {
                 self.walk_expr(l, in_out, loop_scopes);
             }
 
-            ast::expr_swap(l, r) => {
-                self.walk_expr(l, in_out, loop_scopes);
-                self.walk_expr(r, in_out, loop_scopes);
-            }
-
             ast::expr_vec(ref exprs, _) => {
                 self.walk_exprs(*exprs, in_out, loop_scopes)
             }

src/librustc/middle/liveness.rs

@@ -523,7 +523,7 @@ fn visit_expr(expr: @expr, self: @mut IrMaps, vt: vt<@mut IrMaps>) {
       expr_binary(*) | expr_addr_of(*) | expr_copy(*) | expr_loop_body(*) |
       expr_do_body(*) | expr_cast(*) | expr_unary(*) | expr_break(_) |
       expr_again(_) | expr_lit(_) | expr_ret(*) | expr_block(*) |
-      expr_assign(*) | expr_swap(*) | expr_assign_op(*) | expr_mac(*) |
+      expr_assign(*) | expr_assign_op(*) | expr_mac(*) |
       expr_struct(*) | expr_repeat(*) | expr_paren(*) |
       expr_inline_asm(*) => {
           visit::visit_expr(expr, self, vt);
@@ -1141,21 +1141,6 @@ pub impl Liveness {
             self.propagate_through_expr(r, succ)
           }
 
-          expr_swap(l, r) => {
-            // see comment on lvalues in
-            // propagate_through_lvalue_components()
-
-            // I count swaps as `used` cause it might be something like:
-            //    foo.bar <-> x
-            // and I am too lazy to distinguish this case from
-            //    y <-> x
-            // (where both x, y are unused) just for a warning.
-            let succ = self.write_lvalue(r, succ, ACC_WRITE|ACC_READ|ACC_USE);
-            let succ = self.write_lvalue(l, succ, ACC_WRITE|ACC_READ|ACC_USE);
-            let succ = self.propagate_through_lvalue_components(r, succ);
-            self.propagate_through_lvalue_components(l, succ)
-          }
-
           expr_assign_op(_, l, r) => {
             // see comment on lvalues in
             // propagate_through_lvalue_components()
@@ -1533,7 +1518,7 @@ fn check_expr(expr: @expr, self: @Liveness, vt: vt<@Liveness>) {
       expr_vstore(*) | expr_vec(*) | expr_tup(*) | expr_log(*) |
       expr_binary(*) | expr_copy(*) | expr_loop_body(*) | expr_do_body(*) |
       expr_cast(*) | expr_unary(*) | expr_ret(*) | expr_break(*) |
-      expr_again(*) | expr_lit(_) | expr_block(*) | expr_swap(*) |
+      expr_again(*) | expr_lit(_) | expr_block(*) |
       expr_mac(*) | expr_addr_of(*) | expr_struct(*) | expr_repeat(*) |
       expr_paren(*) => {
         visit::visit_expr(expr, self, vt);

src/librustc/middle/mem_categorization.rs

@@ -413,7 +413,7 @@ pub impl mem_categorization_ctxt {
 
           ast::expr_paren(e) => self.cat_expr_unadjusted(e),
 
-          ast::expr_addr_of(*) | ast::expr_call(*) | ast::expr_swap(*) |
+          ast::expr_addr_of(*) | ast::expr_call(*) |
           ast::expr_assign(*) | ast::expr_assign_op(*) |
           ast::expr_fn_block(*) | ast::expr_ret(*) | ast::expr_loop_body(*) |
           ast::expr_do_body(*) | ast::expr_unary(*) |

src/librustc/middle/moves.rs

@@ -650,11 +650,6 @@ pub impl VisitContext {
                 self.consume_expr(count, visitor);
             }
 
-            expr_swap(lhs, rhs) => {
-                self.use_expr(lhs, Read, visitor);
-                self.use_expr(rhs, Read, visitor);
-            }
-
             expr_loop_body(base) |
             expr_do_body(base) => {
                 self.use_expr(base, comp_mode, visitor);

src/librustc/middle/trans/expr.rs

@@ -528,33 +528,6 @@ fn trans_rvalue_stmt_unadjusted(bcx: block, expr: @ast::expr) -> block {
             return src_datum.store_to_datum(
                 bcx, src.id, DROP_EXISTING, dst_datum);
         }
-        ast::expr_swap(dst, src) => {
-            let dst_datum = unpack_datum!(bcx, trans_lvalue(bcx, dst));
-            let src_datum = unpack_datum!(bcx, trans_lvalue(bcx, src));
-
-            // If the source and destination are the same, then don't swap.
-            // Avoids performing an overlapping memcpy
-            let dst_datum_ref = dst_datum.to_ref_llval(bcx);
-            let src_datum_ref = src_datum.to_ref_llval(bcx);
-            let cmp = ICmp(bcx, lib::llvm::IntEQ,
-                           src_datum_ref,
-                           dst_datum_ref);
-
-            let swap_cx = base::sub_block(bcx, "swap");
-            let next_cx = base::sub_block(bcx, "next");
-
-            CondBr(bcx, cmp, next_cx.llbb, swap_cx.llbb);
-
-            let scratch = scratch_datum(swap_cx, dst_datum.ty, false);
-
-            let swap_cx = dst_datum.move_to_datum(swap_cx, INIT, scratch);
-            let swap_cx = src_datum.move_to_datum(swap_cx, INIT, dst_datum);
-            let swap_cx = scratch.move_to_datum(swap_cx, INIT, src_datum);
-
-            Br(swap_cx, next_cx.llbb);
-
-            return next_cx;
-        }
         ast::expr_assign_op(op, dst, src) => {
             return trans_assign_op(bcx, expr, op, dst, src);
         }

src/librustc/middle/trans/type_use.rs

@@ -314,7 +314,7 @@ pub fn mark_for_expr(cx: Context, e: @expr) {
               }
           }
       }
-      expr_assign(val, _) | expr_swap(val, _) | expr_assign_op(_, val, _) |
+      expr_assign(val, _) | expr_assign_op(_, val, _) |
       expr_ret(Some(val)) => {
         node_type_needs(cx, use_repr, val.id);
       }

src/librustc/middle/ty.rs

@@ -3465,7 +3465,6 @@ pub fn expr_kind(tcx: ctxt,
         ast::expr_while(*) |
         ast::expr_loop(*) |
         ast::expr_assign(*) |
-        ast::expr_swap(*) |
         ast::expr_inline_asm(*) |
         ast::expr_assign_op(*) => {
             RvalueStmtExpr

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

@@ -2460,20 +2460,6 @@ pub fn check_expr_with_unifier(fcx: @mut FnCtxt,
             fcx.write_nil(id);
         }
       }
-      ast::expr_swap(lhs, rhs) => {
-        check_assignment(fcx, lhs, rhs, id);
-        let lhs_ty = fcx.expr_ty(lhs);
-        let rhs_ty = fcx.expr_ty(rhs);
-        if ty::type_is_error(lhs_ty) || ty::type_is_error(rhs_ty) {
-            fcx.write_error(id);
-        }
-        else if ty::type_is_bot(lhs_ty) || ty::type_is_bot(rhs_ty) {
-            fcx.write_bot(id);
-        }
-        else {
-            fcx.write_nil(id);
-        }
-      }
       ast::expr_if(cond, ref thn, elsopt) => {
         check_expr_has_type(fcx, cond, ty::mk_bool());
         check_then_else(fcx, thn, elsopt, id, expr.span);

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

@@ -1016,7 +1016,6 @@ pub mod guarantor {
             ast::expr_while(*) |
             ast::expr_loop(*) |
             ast::expr_assign(*) |
-            ast::expr_swap(*) |
             ast::expr_assign_op(*) |
             ast::expr_cast(*) |
             ast::expr_call(*) |

src/librusti/rusti.rc

@@ -96,10 +96,6 @@ fn record(repl: Repl, blk: @ast::blk, intr: @token::ident_interner) -> Repl {
                         match expr.node {
                             ast::expr_assign(*) |
                             ast::expr_assign_op(*) |
-                            ast::expr_swap(*) => {
-                                pprust::print_stmt(pp, *stmt);
-                                writer.write_line(~"");
-                            }
                             _ => {}
                         }
                     }

src/libsyntax/ast.rs

@@ -569,7 +569,6 @@ pub enum expr_ {
 
     expr_copy(@expr),
     expr_assign(@expr, @expr),
-    expr_swap(@expr, @expr),
     expr_assign_op(binop, @expr, @expr),
     expr_field(@expr, ident, ~[@Ty]),
     expr_index(@expr, @expr),

src/libsyntax/fold.rs

@@ -511,9 +511,6 @@ pub fn noop_fold_expr(e: &expr_, fld: @ast_fold) -> expr_ {
         expr_assign(el, er) => {
             expr_assign(fld.fold_expr(el), fld.fold_expr(er))
         }
-        expr_swap(el, er) => {
-            expr_swap(fld.fold_expr(el), fld.fold_expr(er))
-        }
         expr_assign_op(op, el, er) => {
             expr_assign_op(op, fld.fold_expr(el), fld.fold_expr(er))
         }

src/libsyntax/parse/obsolete.rs

@@ -40,6 +40,7 @@ pub enum ObsoleteSyntax {
     ObsoleteModeInFnType,
     ObsoleteMoveInit,
     ObsoleteBinaryMove,
+    ObsoleteSwap,
     ObsoleteUnsafeBlock,
     ObsoleteUnenforcedBound,
     ObsoleteImplSyntax,
@@ -129,6 +130,10 @@ pub impl Parser {
                 "binary move",
                 "Write `foo = move bar` instead"
             ),
+            ObsoleteSwap => (
+                "swap",
+                "Use core::util::{swap, replace} instead"
+            ),
             ObsoleteUnsafeBlock => (
                 "non-standalone unsafe block",
                 "use an inner `unsafe { ... }` block instead"

src/libsyntax/parse/parser.rs

@@ -26,7 +26,7 @@ use ast::{expr_break, expr_call, expr_cast, expr_copy, expr_do_body};
 use ast::{expr_field, expr_fn_block, expr_if, expr_index};
 use ast::{expr_lit, expr_log, expr_loop, expr_loop_body, expr_mac};
 use ast::{expr_method_call, expr_paren, expr_path, expr_repeat};
-use ast::{expr_ret, expr_swap, expr_struct, expr_tup, expr_unary};
+use ast::{expr_ret, expr_struct, expr_tup, expr_unary};
 use ast::{expr_vec, expr_vstore, expr_vstore_mut_box};
 use ast::{expr_vstore_slice, expr_vstore_box};
 use ast::{expr_vstore_mut_slice, expr_while, extern_fn, field, fn_decl};
@@ -70,7 +70,7 @@ use parse::lexer::reader;
 use parse::lexer::TokenAndSpan;
 use parse::obsolete::{ObsoleteClassTraits};
 use parse::obsolete::{ObsoleteLet, ObsoleteFieldTerminator};
-use parse::obsolete::{ObsoleteMoveInit, ObsoleteBinaryMove};
+use parse::obsolete::{ObsoleteMoveInit, ObsoleteBinaryMove, ObsoleteSwap};
 use parse::obsolete::{ObsoleteSyntax, ObsoleteLowerCaseKindBounds};
 use parse::obsolete::{ObsoleteUnsafeBlock, ObsoleteImplSyntax};
 use parse::obsolete::{ObsoleteTraitBoundSeparator, ObsoleteMutOwnedPointer};
@@ -1849,9 +1849,11 @@ pub impl Parser {
                            expr_break(None))
           }
           token::DARROW => {
+            self.obsolete(*self.span, ObsoleteSwap);
             self.bump();
-            let rhs = self.parse_expr();
-            self.mk_expr(lo, rhs.span.hi, expr_swap(lhs, rhs))
+            // Ignore what we get, this is an error anyway
+            self.parse_expr();
+            self.mk_expr(lo, self.span.hi, expr_break(None))
           }
           _ => {
               lhs

src/libsyntax/print/pprust.rs

@@ -1328,12 +1328,6 @@ pub fn print_expr(s: @ps, expr: @ast::expr) {
         word_space(s, ~"=");
         print_expr(s, rhs);
       }
-      ast::expr_swap(lhs, rhs) => {
-        print_expr(s, lhs);
-        space(s.s);
-        word_space(s, ~"<->");
-        print_expr(s, rhs);
-      }
       ast::expr_assign_op(op, lhs, rhs) => {
         print_expr(s, lhs);
         space(s.s);

src/libsyntax/visit.rs

@@ -516,10 +516,6 @@ pub fn visit_expr<E: Copy>(ex: @expr, e: E, v: vt<E>) {
             (v.visit_expr)(a, e, v);
         }
         expr_copy(a) => (v.visit_expr)(a, e, v),
-        expr_swap(a, b) => {
-            (v.visit_expr)(a, e, v);
-            (v.visit_expr)(b, e, v);
-        }
         expr_assign_op(_, a, b) => {
             (v.visit_expr)(b, e, v);
             (v.visit_expr)(a, e, v);