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- Within the constraints based on the top-level types which VMD can parse, the
- libraries gives the end-user the ability to design macros with dynamic data
- types. By this I mean that a macro could be designed to handle different data
- types based on some documented agreement of different combinations of macro
- input meaning slightly different things. Add to this the ability to design
- such macros with variadic parameters and we have a preprocessor system of macro
- creation which to a lesser extent rivals the DSELS of template metaprogramming.
- Of course the preprocessor is not nearly as flexible as C++ templates, but
- still the sort of preprocessor metaprogramming one could do with VMD, and the
- underlying Boost PP, in creating flexible macros which can handle different
- combinations of data types is very interesting.
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- Of course macros need to be usable by an end-user so the syntactical ability
- of sequences to represent different types of input data must be balanced against
- ease of use and understanding when using a macro. But because certain sequences
- can mimic C++ function calls to some extent it is possible to represent macros
- as a language closer to C++ with VMD.
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- <p>
- What is important when designing a macro in which you parse input to decide
- which type of data the invoker is passing to your macro is that you are aware
- of the constraints when parsing a data type. As an example if you design a
- macro where some input can either be a number, an identifier, or some other
- data type top-level input then attempting to parse the data to see if it is
- a number or identifier could fail with a preprocessor error and nullify your
- design if the data is not a VMD data type. So designing a macro with data types
- in mind often means restricting data to parseable top-level types.
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