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For example, the use of the << operator in C++ a << b shifts the bits in the variable a left by b bits if a and b are of an integer type, but if a is an output stream then the above code will attempt to write a b to the stream.
// A class template to express an equality comparison interface. template < typename T > class equal_comparable {friend bool operator == (T const & a, T const & b) {return a. equal_to (b);} friend bool operator!= (T const & a, T const & b) {return! a. equal_to (b);}}; // Class value_type wants to have == and !=, so it derives from // equal_comparable with itself as argument (which is the CRTP ...
In this example, the indexer is used to get the value at the nth position, and then to get the position in the list referenced by its value. The output of the code is: John is the member number 0 of the doeFamily Jane is the member number 1 of the doeFamily
In languages that support operator overloading by the programmer (such as C++) but have a limited set of operators, operator overloading is often used to define customized uses for operators. In the example IF ORDER_DATE > "12/31/2011" AND ORDER_DATE < "01/01/2013" THEN CONTINUE ELSE STOP, the operators are: > (greater than), AND and < (less than).
All logical operators exist in C and C++ and can be overloaded in C++, albeit the overloading of the logical AND and logical OR is discouraged, because as overloaded operators they behave as ordinary function calls, which means that both of their operands are evaluated, so they lose their well-used and expected short-circuit evaluation property ...
This is an example of overloading or more specifically, operator overloading. Note the ambiguity in the string types used in the last case. Consider "123" + "456" in which the programmer might naturally assume addition rather than concatenation. They may expect "579" instead of "123456". Overloading can therefore provide different meaning, or ...
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Expression templates allow users to approximate the syntax of extended Backus–Naur form (EBNF) completely in C++. Parser objects are composed through operator overloading and the result is a backtracking LL(∞) parser that is capable of parsing rather ambiguous grammars. Spirit can be used for both lexing and parsing, together or separately.