feat(pipe): use pipe status propagation

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);
   }
 };