diff --git a/src/librustc/traits/util.rs b/src/librustc/traits/util.rs
index 0b7526dd78428..940cf736012ec 100644
--- a/src/librustc/traits/util.rs
+++ b/src/librustc/traits/util.rs
@@ -103,11 +103,10 @@ pub fn elaborate_trait_ref<'cx, 'gcx, 'tcx>(
 
 pub fn elaborate_trait_refs<'cx, 'gcx, 'tcx>(
     tcx: TyCtxt<'cx, 'gcx, 'tcx>,
-    trait_refs: &[ty::PolyTraitRef<'tcx>])
+    trait_refs: impl Iterator<Item = ty::PolyTraitRef<'tcx>>)
     -> Elaborator<'cx, 'gcx, 'tcx>
 {
-    let predicates = trait_refs.iter()
-                               .map(|trait_ref| trait_ref.to_predicate())
+    let predicates = trait_refs.map(|trait_ref| trait_ref.to_predicate())
                                .collect();
     elaborate_predicates(tcx, predicates)
 }
@@ -271,7 +270,7 @@ pub fn supertraits<'cx, 'gcx, 'tcx>(tcx: TyCtxt<'cx, 'gcx, 'tcx>,
 }
 
 pub fn transitive_bounds<'cx, 'gcx, 'tcx>(tcx: TyCtxt<'cx, 'gcx, 'tcx>,
-                                          bounds: &[ty::PolyTraitRef<'tcx>])
+                                          bounds: impl Iterator<Item = ty::PolyTraitRef<'tcx>>)
                                           -> Supertraits<'cx, 'gcx, 'tcx>
 {
     elaborate_trait_refs(tcx, bounds).filter_to_traits()
diff --git a/src/librustc_typeck/astconv.rs b/src/librustc_typeck/astconv.rs
index 1978f86545e7b..7ddc56974d816 100644
--- a/src/librustc_typeck/astconv.rs
+++ b/src/librustc_typeck/astconv.rs
@@ -1112,12 +1112,12 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx>+'o {
     {
         let tcx = self.tcx();
 
-        let bounds: Vec<_> = self.get_type_parameter_bounds(span, ty_param_def_id)
-            .predicates.into_iter().filter_map(|(p, _)| p.to_opt_poly_trait_ref()).collect();
+        let bounds = self.get_type_parameter_bounds(span, ty_param_def_id)
+            .predicates.into_iter().filter_map(|(p, _)| p.to_opt_poly_trait_ref());
 
         // Check that there is exactly one way to find an associated type with the
         // correct name.
-        let suitable_bounds = traits::transitive_bounds(tcx, &bounds)
+        let suitable_bounds = traits::transitive_bounds(tcx, bounds)
             .filter(|b| self.trait_defines_associated_type_named(b.def_id(), assoc_name));
 
         let param_node_id = tcx.hir.as_local_node_id(ty_param_def_id).unwrap();
diff --git a/src/librustc_typeck/check/method/probe.rs b/src/librustc_typeck/check/method/probe.rs
index c506f23078f25..2202c1d78476b 100644
--- a/src/librustc_typeck/check/method/probe.rs
+++ b/src/librustc_typeck/check/method/probe.rs
@@ -31,6 +31,7 @@ use rustc::middle::stability;
 use syntax::ast;
 use syntax::util::lev_distance::{lev_distance, find_best_match_for_name};
 use syntax_pos::{Span, symbol::Symbol};
+use std::iter;
 use std::mem;
 use std::ops::Deref;
 use std::rc::Rc;
@@ -627,7 +628,7 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
         // itself. Hence, a `&self` method will wind up with an
         // argument type like `&Trait`.
         let trait_ref = principal.with_self_ty(self.tcx, self_ty);
-        self.elaborate_bounds(&[trait_ref], |this, new_trait_ref, item| {
+        self.elaborate_bounds(iter::once(trait_ref), |this, new_trait_ref, item| {
             let new_trait_ref = this.erase_late_bound_regions(&new_trait_ref);
 
             let (xform_self_ty, xform_ret_ty) =
@@ -645,7 +646,7 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
                                                param_ty: ty::ParamTy) {
         // FIXME -- Do we want to commit to this behavior for param bounds?
 
-        let bounds: Vec<_> = self.param_env
+        let bounds = self.param_env
             .caller_bounds
             .iter()
             .filter_map(|predicate| {
@@ -667,10 +668,9 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
                     ty::Predicate::TypeOutlives(..) |
                     ty::Predicate::ConstEvaluatable(..) => None,
                 }
-            })
-            .collect();
+            });
 
-        self.elaborate_bounds(&bounds, |this, poly_trait_ref, item| {
+        self.elaborate_bounds(bounds, |this, poly_trait_ref, item| {
             let trait_ref = this.erase_late_bound_regions(&poly_trait_ref);
 
             let (xform_self_ty, xform_ret_ty) =
@@ -693,15 +693,16 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
 
     // Do a search through a list of bounds, using a callback to actually
     // create the candidates.
-    fn elaborate_bounds<F>(&mut self, bounds: &[ty::PolyTraitRef<'tcx>], mut mk_cand: F)
+    fn elaborate_bounds<F>(&mut self,
+                           bounds: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
+                           mut mk_cand: F)
         where F: for<'b> FnMut(&mut ProbeContext<'b, 'gcx, 'tcx>,
                                ty::PolyTraitRef<'tcx>,
                                ty::AssociatedItem)
     {
-        debug!("elaborate_bounds(bounds={:?})", bounds);
-
         let tcx = self.tcx;
         for bound_trait_ref in traits::transitive_bounds(tcx, bounds) {
+            debug!("elaborate_bounds(bound_trait_ref={:?})", bound_trait_ref);
             for item in self.impl_or_trait_item(bound_trait_ref.def_id()) {
                 if !self.has_applicable_self(&item) {
                     self.record_static_candidate(TraitSource(bound_trait_ref.def_id()));