The C# and C++ language provide ways to introduce shorter names for things. These shortcuts do not have their own identities; they merely let one name be used as a shorthand for the other thing.<\/p>\n
\/\/ C#\r\nusing Console = System.Console;\r\n\r\n\/\/ C++\r\nusing Project = Contoso::Project;\r\n<\/pre>\nThe C# and C++ programming languages call these aliases<\/i>. You are allowing an existing type to go by a different name. It does not create a new type, and the new name is interchangeable with the old one.<\/p>\n
\/\/ C++\r\nextern void UpdateProject(Contoso::Project& project);\r\n\r\nvoid example()\r\n{\r\n Project project;\r\n UpdateProject(project); \/\/ this works\r\n}\r\n<\/pre>\nSimilarly, when you import a namespace with a
using<\/code> directive, the names from the other namespace are visible in your namespace, but they still belong to that other namespace.\u00b9<\/p>\n\/\/ C++\r\nnamespace Other\r\n{\r\n struct OtherStruct;\r\n}\r\n\r\nnamespace Mine\r\n{\r\n using namespace Other;\r\n}\r\n\r\nvoid Welcome(Mine::OtherStruct s);\r\n<\/pre>\nThe signature of the
Welcome<\/code> function isvoid Welcome(Other::OtherStruct)<\/code>, notvoid Welcome(Mine::OtherStruct)<\/code>.<\/p>\nThis trick also gives you a way to switch easily between two options:<\/p>\n
#ifdef USE_CONTOSO_WIDGET\r\nusing Widget = Contoso::Widget;\r\n#else\r\nusing Widget = LitWare::Widget;\r\n#endif\r\n\r\n\/\/ code that uses Widget without caring whose widget it is\r\n<\/pre>\nThe fact that these aliases do not introduce new types means that when you go looking in the debugger, you will see the symbols decorated with their original<\/i> names. Which can be both a good thing and a bad thing.<\/p>\n
It’s a good thing if you want the original name to be the one seen by the outside world. For example, you might create aliases for commonly-used types in your component, but you want people outside your component to use the original names.<\/p>\n
\/\/ component.h\r\n\r\nnamespace Component\r\n{\r\n struct ReversibleWidget;\r\n\r\n void CheckPolarity(ReversibleWidget const&);\r\n}\r\n\r\n\/\/ component.cpp (implementation)\r\n#include<component.h>\r\n\r\nusing FlipWidget = Component::ReversibleWidget;\r\n\r\nvoid Component::CheckPolarity(FlipWidget const& widget)\r\n{\r\n ... do stuff ...\r\n}\r\n<\/pre>\nInside your component, you’d rather just call it a
FlipWidget<\/code>, because that was the internal code name when the product was being developed, and then later, management decided that its public name should beReversibleWidget<\/code>. You can create an alias that lets you continue using your internal code name, so you don’t have to perform a massive search-and-replace across the entire code base (and deal with all the merge conflicts that will inevitably arise).<\/p>\nThat the symbols are decorated with the original names can be a bad thing if the original name is an unwieldy mess, which is unfortunately the case with many classes in the C++ standard library.<\/p>\n
In the C++ standard library,
string<\/code> is an alias forbasic_string<char, std::char_traits<char>, std::allocator<char> ><\/code>,\u00b2 so a function like<\/p>\nvoid FillLookupTable(std::map<std::string, std::string>& table);\r\n<\/pre>\nformally has the signature (deep breath)<\/p>\n
FillLookupTable(std::map<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >&):\r\n<\/pre>\nGood luck typing that into a debugger.<\/p>\n