fix typos and blanks

Author: daixtrose

polymorphism/README.md

@@ -171,7 +171,7 @@ As an alternative, the *definition* of `consume` could be in the header `include
 
 ## Testing
 
-In this example, I use [µt](https://github.com/boost-ext/ut) as testing framework for no good reason. It looks promising and lightweight, and it was written by [Krzysztof Jusiak](https://github.com/krzysztof-jusiak) whom I adore for his outstanding C++ programming skills and his [C++ Tip of The Week](https://github.com/tip-of-the-week/cpp) collection of crazy C++ riddles.   
+In this example, I use [µt](https://github.com/boost-ext/ut) as testing framework for no good reason. It looks promising and lightweight, and it was written by [Krzysztof Jusiak](https://github.com/krzysztof-jusiak) whom I adore for his outstanding C++ programming skills and his [C++ Tip of The Week](https://github.com/tip-of-the-week/cpp) collection of crazy C++ riddles.
 
 The one-header version of it is pulled into the project via the CMake call
 

polymorphism/include/polymorphism/impl_with_interface.hpp

@@ -1,5 +1,5 @@
-#ifndef POYMORPHISM_IMPL_WITH_INTERFACE_HPP
-#define POYMORPHISM_IMPL_WITH_INTERFACE_HPP
+#ifndef POLYMORPHISM_IMPL_WITH_INTERFACE_HPP
+#define POLYMORPHISM_IMPL_WITH_INTERFACE_HPP
 
 // make the inteface defintion visible
 #include <polymorphism/i_super_cool_features.hpp>
@@ -23,4 +23,4 @@ class Impl
 
 } // namespace classic
 
-#endif // POYMORPHISM_IMPL_WITH_INTERFACE_HPP
+#endif // POLYMORPHISM_IMPL_WITH_INTERFACE_HPP

polymorphism/include/polymorphism/impl_without_interface.hpp

@@ -1,5 +1,5 @@
-#ifndef POYMORPHISM_IMPL_WITHOUT_INTERFACE_HPP
-#define POYMORPHISM_IMPL_WITHOUT_INTERFACE_HPP
+#ifndef POLYMORPHISM_IMPL_WITHOUT_INTERFACE_HPP
+#define POLYMORPHISM_IMPL_WITHOUT_INTERFACE_HPP
 
 #include <polymorphism/has_super_cool_features.hpp>
 
@@ -12,7 +12,7 @@ class Impl {
     std::string s_ { "<default value>" }; // with default member initializer (C++11)
 
 public:
-    std::string coolFeature() const noexcept { return s_; }
+    [[nodiscard]] std::string coolFeature() const noexcept { return s_; }
     void set(std::string s) noexcept
     {
         s_ = std::move(s);
@@ -25,4 +25,4 @@ static_assert(has_super_cool_features<Impl>,
 
 } // namespace modern
 
-#endif // POYMORPHISM_IMPL_WITHOUT_INTERFACE_HPP
+#endif // POLYMORPHISM_IMPL_WITHOUT_INTERFACE_HPP