diff --git a/CMakeLists.txt b/CMakeLists.txt
index 264d9bc..a55502f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,6 +1,6 @@
 cmake_minimum_required(VERSION 3.20)
 include(cmake/color.cmake)
-set(BLT_VERSION 2.0.3)
+set(BLT_VERSION 2.0.4)
 
 set(BLT_TARGET BLT)
 
diff --git a/include/blt/iterator/common.h b/include/blt/iterator/common.h
index 4ffc5ea..ce2805d 100644
--- a/include/blt/iterator/common.h
+++ b/include/blt/iterator/common.h
@@ -25,6 +25,8 @@
 #include <blt/iterator/fwddecl.h>
 #include <blt/meta/meta.h>
 #include <blt/meta/iterator.h>
+#include <functional>
+#include <optional>
 
 namespace blt::iterator
 {
@@ -110,7 +112,7 @@ namespace blt::iterator
             }
         
         protected:
-            Iter iter;
+            mutable Iter iter;
     };
     
     template<typename Iter, typename Derived>
@@ -167,13 +169,15 @@ namespace blt::iterator
             using pointer = value_type;
             using reference = value_type;
             
-            map_wrapper(Iter iter, Func func): deref_only_wrapper<Iter, map_wrapper<Iter, Func>>(std::move(iter)), func(std::move(func))
+            map_wrapper(Iter iter, Func func):
+                    deref_only_wrapper<Iter, map_wrapper<Iter, Func>>(std::move(iter)), func(std::move(func))
             {}
             
             reference operator*() const
             {
                 return func(*this->iter);
             }
+        
         private:
             Func func;
     };
@@ -183,19 +187,27 @@ namespace blt::iterator
     {
         public:
             using iterator_category = typename std::iterator_traits<Iter>::iterator_category;
-            using value_type = meta::deref_return_t<Iter>;
+            using value_type = std::conditional_t<
+                    std::is_reference_v<meta::deref_return_t<Iter>>,
+                    std::optional<std::reference_wrapper<std::remove_reference_t<meta::deref_return_t<Iter>>>>,
+                    std::optional<meta::deref_return_t<Iter>>>;
             using difference_type = blt::ptrdiff_t;
             using pointer = value_type;
             using reference = value_type;
             
-            filter_wrapper(Iter iter, Pred func): deref_only_wrapper<Iter, filter_wrapper<Iter, Pred>>(std::move(iter)), func(std::move(func))
+            filter_wrapper(Iter iter, Pred func):
+                    deref_only_wrapper<Iter, filter_wrapper<Iter, Pred>>(std::move(iter)), func(std::move(func))
             {}
             
             reference operator*() const
             {
-                
-                return func(*this->iter);
+                if (!func(*this->iter))
+                {
+                    return {};
+                }
+                return *this->iter;
             }
+        
         private:
             Pred func;
     };
@@ -346,13 +358,21 @@ namespace blt::iterator
             }
             
             template<typename Func>
-            auto map(Func func)
+            auto map(Func func) const
             {
                 return iterator_container<blt::iterator::map_wrapper<IterBase, Func>>{
                         blt::iterator::map_wrapper<IterBase, Func>{m_begin, func},
                         blt::iterator::map_wrapper<IterBase, Func>{m_end, func}};
             }
             
+            template<typename Pred>
+            auto filter(Pred pred) const
+            {
+                return iterator_container<blt::iterator::filter_wrapper<IterBase, Pred>>{
+                        blt::iterator::filter_wrapper<IterBase, Pred>{m_begin, pred},
+                        blt::iterator::filter_wrapper<IterBase, Pred>{m_end, pred}};
+            }
+            
             auto begin() const
             {
                 return m_begin;
diff --git a/libraries/parallel-hashmap b/libraries/parallel-hashmap
index 7ef2e73..93201da 160000
--- a/libraries/parallel-hashmap
+++ b/libraries/parallel-hashmap
@@ -1 +1 @@
-Subproject commit 7ef2e733416953b222851f9a360d7fc72d068ee5
+Subproject commit 93201da2ba5a6aba0a6e57ada64973555629b3e3
diff --git a/tests/iterator_tests.cpp b/tests/iterator_tests.cpp
index 9323d1e..66f787f 100644
--- a/tests/iterator_tests.cpp
+++ b/tests/iterator_tests.cpp
@@ -196,6 +196,58 @@ void test_iterate()
         auto [a, b] = data;
         BLT_TRACE_STREAM << "Map + Zip + Skip + Take + Enumerate (Index: " << i << ")> " << a << " " << b << "\n";
     }
+    BLT_TRACE("================================");
+    for (auto [i, data] : blt::iterate(array_1).map(
+            [](const blt::vec2& in) {
+                return in.normalize();
+            }).zip(list_1).skip(3).take(4).enumerate())
+    {
+        auto [a, b] = data;
+        BLT_TRACE_STREAM << "Map + Zip + Skip + Take + Enumerate (Index: " << i << ")> " << a << " " << b << "\n";
+    }
+    BLT_TRACE("================================");
+    for (auto a : blt::iterate(array_1).map([](const blt::vec2& in) { return in.normalize(); })
+                                       .filter([](const blt::vec2& f) { return f.x() > 0.5; }))
+    {
+        if (!a)
+            continue;
+        auto v = *a;
+        BLT_TRACE_STREAM << " So this one works? " << v << "\n";
+    }
+    BLT_TRACE("================================");
+    for (auto a : blt::iterate(array_1).map([](const blt::vec2& in) { return in.normalize(); })
+                                       .enumerate().filter([](const auto& f) { return f.value.x() > 0.5; }))
+    {
+        if (!a)
+            continue;
+        auto [index, v] = *a;
+        BLT_TRACE_STREAM << " So this one works? (" << index << ")" << v << "\n";
+    }
+    BLT_TRACE("================================");
+//    for (auto a : blt::iterate(array_1).filter([](const auto& f) { return f.x() > 3 && f.y() < 6; }).take(2))
+//    {
+//        if (!a)
+//            continue;
+//        auto v = *a;
+//        BLT_TRACE_STREAM << " How about this one?? " << v.get() << "\n";
+//    }
+    for (auto a : blt::iterate(array_1).map([](const auto& f) { return f.x() > 3 && f.y() < 6; }))
+    {
+        BLT_TRACE_STREAM << " How about this one?? " << a << "\n";
+    }
+
+//    for (auto [value, a] : blt::iterate(array_1).map(
+//            [](const blt::vec2& in) {
+//                return in.normalize();
+//            }).enumerate().filter([](const auto& v) {
+//                return v.index % 2 == 0;
+//            }).zip(array_2).skip(3))
+//    {
+//        if (!value)
+//            continue;
+//        auto [i, v] = *value;
+//        BLT_TRACE_STREAM << "Enumerate Filter (Index: " << i << ")> " << v << "\n";
+//    }
 }
 
 int main()