New cpp folder structure

Signed-off-by: Alexander Borsuk <me@alex.bio>

libs/base/control_flow.hpp

@@ -0,0 +1,44 @@
+#pragma once
+
+#include <type_traits>
+
+namespace base
+{
+// This enum is used to control the flow of ForEach invocations.
+enum class ControlFlow
+{
+  Break,
+  Continue
+};
+
+// A wrapper that calls |fn| with arguments |args|.
+// To avoid excessive calls, |fn| may signal the end of execution via its return value,
+// which should then be checked by the wrapper's user.
+template <typename Fn>
+class ControlFlowWrapper
+{
+public:
+  template <typename Gn>
+  explicit ControlFlowWrapper(Gn && gn) : m_fn(std::forward<Gn>(gn))
+  {
+  }
+
+  template <typename... Args>
+  std::enable_if_t<std::is_same_v<std::invoke_result_t<Fn, Args...>, ControlFlow>, ControlFlow>
+  operator()(Args &&... args)
+  {
+    return m_fn(std::forward<Args>(args)...);
+  }
+
+  template <typename... Args>
+  std::enable_if_t<std::is_same_v<std::invoke_result_t<Fn, Args...>, void>, ControlFlow>
+  operator()(Args &&... args)
+  {
+    m_fn(std::forward<Args>(args)...);
+    return ControlFlow::Continue;
+  }
+
+private:
+  Fn m_fn;
+};
+}  // namespace base