From fbab07f9b3dac90ce2136506f72879335193fc02 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Sun, 27 Jan 2019 00:44:45 +0100
Subject: [PATCH] [iter] Add hb_bool() and make hb_filter default to it for
 predicate

---
 src/hb-algs.hh   |  6 ++++++
 src/hb-iter.hh   |  4 ++--
 src/test-iter.cc | 10 +++++++++-
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/src/hb-algs.hh b/src/hb-algs.hh
index a0896dda9..bd03a74ea 100644
--- a/src/hb-algs.hh
+++ b/src/hb-algs.hh
@@ -41,6 +41,12 @@ static HB_UNUSED const struct hb_identity_ft
   operator () (const T& v) const { return v; }
 } hb_identity;
 
+static HB_UNUSED const struct hb_bool_ft
+{
+  template <typename T> bool
+  operator () (const T& v) const { return bool (v); }
+} hb_bool;
+
 template <typename T1, typename T2>
 struct hb_pair_t
 {
diff --git a/src/hb-iter.hh b/src/hb-iter.hh
index eff4e2833..57a687af4 100644
--- a/src/hb-iter.hh
+++ b/src/hb-iter.hh
@@ -281,9 +281,9 @@ struct hb_filter_iter_factory_t
   Pred p;
   Proj f;
 };
-template <typename Pred, typename Proj = const hb_identity_ft&>
+template <typename Pred = const hb_bool_ft&, typename Proj = const hb_identity_ft&>
 inline hb_filter_iter_factory_t<Pred, Proj>
-hb_filter (Pred&& p, Proj&& f = hb_identity)
+hb_filter (Pred&& p = hb_bool, Proj&& f = hb_identity)
 { return hb_filter_iter_factory_t<Pred, Proj> (p, f); }
 
 /* hb_zip() */
diff --git a/src/test-iter.cc b/src/test-iter.cc
index 567da72d5..97a739cd2 100644
--- a/src/test-iter.cc
+++ b/src/test-iter.cc
@@ -84,7 +84,8 @@ test_iterator (Iter it)
 
   assert (*it == it[0]);
 
-  if (it.is_random_access_iterator) {}
+  static_assert (true || it.is_random_access_iterator, "");
+  static_assert (true || it.is_sorted_iterator, "");
 }
 
 template <typename Iterable,
@@ -134,5 +135,12 @@ main (int argc, char **argv)
   hb_array_t<hb_vector_t<int> > pa;
   pa->as_array ();
 
+  s
+  | hb_map (hb_identity)
+  | hb_filter ()
+  | hb_filter (hb_bool)
+  | hb_filter (hb_bool, hb_identity)
+  ;
+
   return 0;
 }