Remove allocation in push_type_params

Author: Mark-Simulacrum

src/librustc_trans/trans_item.rs

@@ -36,6 +36,7 @@ use glue;
 use abi::{Abi, FnType};
 use back::symbol_names;
 use std::fmt::Write;
+use std::iter;
 
 #[derive(PartialEq, Eq, Clone, Copy, Debug, Hash)]
 pub enum TransItem<'tcx> {
@@ -410,7 +411,7 @@ impl<'a, 'tcx> DefPathBasedNames<'a, 'tcx> {
             ty::TyFloat(ast::FloatTy::F64) => output.push_str("f64"),
             ty::TyAdt(adt_def, substs) => {
                 self.push_def_path(adt_def.did, output);
-                self.push_type_params(substs, &[], output);
+                self.push_type_params(substs, iter::empty(), output);
             },
             ty::TyTuple(component_types) => {
                 output.push('(');
@@ -461,7 +462,7 @@ impl<'a, 'tcx> DefPathBasedNames<'a, 'tcx> {
                 if let Some(principal) = trait_data.principal() {
                     self.push_def_path(principal.def_id(), output);
                     self.push_type_params(principal.skip_binder().substs,
-                        &trait_data.projection_bounds().collect::<Vec<_>>()[..],
+                        trait_data.projection_bounds(),
                         output);
                 }
             },
@@ -513,7 +514,7 @@ impl<'a, 'tcx> DefPathBasedNames<'a, 'tcx> {
                 self.push_def_path(def_id, output);
                 let generics = self.tcx.item_generics(self.tcx.closure_base_def_id(def_id));
                 let substs = closure_substs.substs.truncate_to(self.tcx, generics);
-                self.push_type_params(substs, &[], output);
+                self.push_type_params(substs, iter::empty(), output);
             }
             ty::TyError |
             ty::TyInfer(_) |
@@ -553,11 +554,14 @@ impl<'a, 'tcx> DefPathBasedNames<'a, 'tcx> {
         output.pop();
     }
 
-    pub fn push_type_params(&self,
+    fn push_type_params<I>(&self,
                             substs: &Substs<'tcx>,
-                            projections: &[ty::PolyExistentialProjection<'tcx>],
-                            output: &mut String) {
-        if substs.types().next().is_none() && projections.is_empty() {
+                            projections: I,
+                            output: &mut String)
+        where I: Iterator<Item=ty::PolyExistentialProjection<'tcx>>
+    {
+        let mut projections = projections.peekable();
+        if substs.types().next().is_none() && projections.peek().is_none() {
             return;
         }
 
@@ -587,6 +591,6 @@ impl<'a, 'tcx> DefPathBasedNames<'a, 'tcx> {
                                    instance: Instance<'tcx>,
                                    output: &mut String) {
         self.push_def_path(instance.def, output);
-        self.push_type_params(instance.substs, &[], output);
+        self.push_type_params(instance.substs, iter::empty(), output);
     }
 }