Make it possible to apply transformations through pipes

include/continuable/continuable-base.hpp

@@ -392,6 +392,22 @@ public:
     return std::move(*this).then(std::forward<T>(right));
   }
 
+  /// The pipe operator | is an alias for the continuable::apply method.
+  ///
+  /// \param transform The transformer which is applied.
+  ///
+  /// \returns See the corresponding continuable_base::apply method for the
+  ///          explanation of the return type.
+  ///
+  /// \note    You may create your own transformation through
+  ///          calling make_transformation.
+  ///
+  /// \since 3.0.0
+  template <typename T>
+  auto operator|(detail::types::transform<T> transform) && {
+    return std::move(*this).apply(std::move(transform));
+  }
+
   /// Invokes both continuable_base objects parallel and calls the
   /// callback with the result of both continuable_base objects.
   ///

include/continuable/continuable-transforms.hpp

@@ -32,8 +32,23 @@
 #define CONTINUABLE_TRANSFORMS_HPP_INCLUDED
 
 #include <continuable/detail/transforms.hpp>
+#include <continuable/detail/types.hpp>
 
 namespace cti {
+/// A callable tag object which marks a wrapped callable object
+/// as continuable transformation which enables some useful overloads.
+///
+/// \since 3.0.0
+using detail::types::transform;
+
+/// Wraps the given callable object into a transform class.
+///
+/// \since 3.0.0
+template <typename T>
+auto make_transform(T&& callable) {
+  return transform<std::decay_t<T>>(std::forward<T>(callable));
+}
+
 /// The namespace transforms declares callable objects that transform
 /// any continuable_base to an object or to a continuable_base itself.
 ///
@@ -61,10 +76,10 @@ namespace transforms {
 ///
 /// \since 2.0.0
 inline auto futurize() {
-  return [](auto&& continuable) {
+  return make_transform([](auto&& continuable) {
     using detail::transforms::as_future;
     return as_future(std::forward<decltype(continuable)>(continuable));
-  };
+  });
 }
 
 /// Returns a transform that if applied to a continuable, it will ignores all
@@ -77,9 +92,9 @@ inline auto futurize() {
 ///
 /// \since 2.0.0
 inline auto flatten() {
-  return [](auto&& continuable) {
+  return make_transform([](auto&& continuable) {
     return std::forward<decltype(continuable)>(continuable).fail([](auto&&) {});
-  };
+  });
 }
 } // namespace transforms
 } // namespace cti

include/continuable/detail/types.hpp

@@ -31,6 +31,8 @@
 #ifndef CONTINUABLE_DETAIL_TYPES_HPP_INCLUDED
 #define CONTINUABLE_DETAIL_TYPES_HPP_INCLUDED
 
+#include <utility>
+
 #include <continuable/detail/features.hpp>
 
 #ifndef CONTINUABLE_WITH_CUSTOM_ERROR_TYPE
@@ -65,6 +67,16 @@ struct this_thread_executor_tag {};
 /// A tag which is used to continue with an error
 struct dispatch_error_tag {};
 
+/// Marks a given callable object as transformation
+template <typename T>
+class transform : T {
+public:
+  explicit transform(T callable) : T(std::move(callable)) {
+  }
+
+  using T::operator();
+};
+
 } // namespace types
 } // namespace detail
 } // namespace cti

test/unit-test/multi/test-continuable-transforms.cpp

@@ -56,12 +56,10 @@ TYPED_TEST(single_dimension_tests, are_convertible_to_futures) {
   {
     auto canary = std::make_tuple(0xFD, 0xF5);
 
-    auto future = this->supply()
-                      .then([&] {
-                        // ...
-                        return canary;
-                      })
-                      .apply(cti::transforms::futurize());
+    auto future = this->supply().then([&] {
+      // ...
+      return canary;
+    }) | cti::transforms::futurize();
 
     ASSERT_TRUE(is_ready(future));
     EXPECT_EQ(future.get(), canary);