Merge pull request #3629 from zwhitchcox/patch-2

Update value-types-modern-cpp.md

Author: ktoliver

docs/cpp/value-types-modern-cpp.md

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 # C++ classes as value types
 
-C++ classes are by default value types. They can be specified as reference types, which enable polymorphic behavior to support object-oriented programming. Value types are sometimes viewed from the perspective of memory and layout control, whereas reference types are about base classes and virtual functions for polymorphic purposes. By default, value types are copyable, which means there is always a copy constructor and a copy assignment operator. For reference types, you make the class non-copyable (disable the copy constructor and copy assignment operator) and use a virtual destructor, which supports their intended polymorphism. Value types are also about the contents, which, when they are copied, always give you two independent values that can be modified separately. Reference types are about identity - what kind of object is it? For this reason, "reference types" are also referred to as "polymorphic types".
+C++ classes are, by default, value types. They can be specified as reference types, which enable polymorphic behavior to support object-oriented programming. Value types are sometimes viewed from the perspective of memory and layout control, whereas reference types are about base classes and virtual functions for polymorphic purposes. By default, value types are copyable, which means there is always a copy constructor and a copy assignment operator. For reference types, you make the class non-copyable (disable the copy constructor and copy assignment operator) and use a virtual destructor, which supports their intended polymorphism. Value types are also about the contents, which, when they are copied, always give you two independent values that can be modified separately. Reference types are about identity - what kind of object is it? For this reason, "reference types" are also referred to as "polymorphic types".
 
 If you really want a reference-like type (base class, virtual functions), you need to explicitly disable copying, as shown in the `MyRefType` class in the following code.