feat(pipe): use pipe status propagation

include/mosh-me/pipeline.hpp

@@ -1,18 +1,19 @@
 #pragma once
+#include <expected>
 #include <memory>
-#include <optional>
 
 namespace mosh_me {
 
-template <typename A, typename B>
-concept AttachableTo = requires {
-  typename A::output_type;
-  typename B::input_type;
-} && std::convertible_to<typename A::output_type, typename B::input_type>;
+enum class PipeStatus {
+  NO_INPUT_ATTACHED,
+  PIPE_EOF,
+};
+
+template <typename Data> using PipeData = std::expected<Data, PipeStatus>;
 
 template <typename Output> class PipeOutput {
 public:
-  virtual std::optional<Output> pull() noexcept = 0;
+  virtual PipeData<Output> pull() noexcept = 0;
 };
 
 template <typename Input> class PipeInput {
@@ -20,7 +21,7 @@ private:
   std::shared_ptr<PipeOutput<Input>> input_;
 
 protected:
-  std::optional<Input> fetchInput() { return input_->pull(); }
+  PipeData<Input> fetchInput() { return input_->pull(); }
 
 public:
   void linkInput(std::shared_ptr<PipeOutput<Input>> input) { input_ = input; };
@@ -35,11 +36,11 @@ public:
 
   PipeSource(std::shared_ptr<PipeOutput<Output>> p) : source_(p) {}
 
-  std::optional<Output> pull() {
+  PipeData<Output> pull() {
     if (source_) {
       return source_->pull();
     } else {
-      return std::nullopt;
+      return std::unexpected(PipeStatus::NO_INPUT_ATTACHED);
     }
   }
 };
@@ -67,7 +68,8 @@ public:
   }
 };
 
-template <typename PipeType, typename O> class AsPipeSource {
+template <typename PipeType, typename O>
+class AsPipeSource : public PipeOutput<O> {
 public:
   template <typename... Args> static PipeSource<O> link(Args &&...args) {
     return PipeSource<O>(
@@ -75,7 +77,8 @@ public:
   }
 };
 
-template <typename PipeType, typename I, typename O> class AsPipeLink {
+template <typename PipeType, typename I, typename O>
+class AsPipeLink : public PipeWorker<I, O> {
 public:
   template <typename... Args> static PipeLink<I, O> link(Args &&...args) {
     return PipeLink<I, O>(

test/pipeline.cpp

@@ -5,59 +5,55 @@
 
 using namespace mosh_me;
 
-class CountProducer : public PipeOutput<int>,
-                      public AsPipeSource<CountProducer, int> {
+class CountProducer : public AsPipeSource<CountProducer, int> {
 private:
   int counter_ = 0;
 
 public:
-  std::optional<int> pull() noexcept override {
+  PipeData<int> pull() noexcept override {
     if (auto i = counter_++; i < 10) {
       return i;
     } else {
-      return std::nullopt;
+      return std::unexpected(PipeStatus::PIPE_EOF);
     }
   }
 };
 
-class Doubler : public PipeWorker<int, int>,
-                public AsPipeLink<Doubler, int, int> {
+class Doubler : public AsPipeLink<Doubler, int, int> {
 public:
-  std::optional<int> pull() noexcept override {
-    return fetchInput().and_then(
-        [](int x) { return std::make_optional(x * 2); });
+  PipeData<int> pull() noexcept override {
+    return fetchInput().and_then([](int x) -> PipeData<int> { return x * 2; });
   }
 };
 
-class Multiplier : public PipeWorker<int, int>,
-                   public AsPipeLink<Multiplier, int, int> {
+class Multiplier : public AsPipeLink<Multiplier, int, int> {
   int f_;
 
 public:
   Multiplier(int f) : f_(f) {}
-  std::optional<int> pull() noexcept override {
+  PipeData<int> pull() noexcept override {
     return fetchInput().and_then(
-        [this](int x) { return std::make_optional(f_ * x); });
+        [this](int x) -> PipeData<int> { return f_ * x; });
   }
 };
 
-class Sum2 : public PipeWorker<int, int>, public AsPipeLink<Sum2, int, int> {
+class Sum2 : public AsPipeLink<Sum2, int, int> {
 private:
   std::optional<int> last_;
 
 public:
-  std::optional<int> pull() noexcept override {
+  PipeData<int> pull() noexcept override {
     if (auto x = fetchInput(); x) {
       if (last_) {
         auto sum = *last_ + *x;
         last_ = std::nullopt;
         return sum;
       } else {
-        last_ = x;
+        last_ = *x;
         return pull();
       }
     }
-    return std::nullopt;
+    return std::unexpected(PipeStatus::PIPE_EOF);
   }
 };