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Showing posts from 2009

Modifying temporaries

Temporary objects are created and destroyed all the time in a C++ program. A simple example would be a function that returns by value. A temporary is as good as a const object because it makes little sense (usually) to change a temporary object, which is unnamed and has a very short time span. (Note: A temporary can be bound to a const reference in which case the scope of the temporary is the same as that of the reference.) However, as it turns out, in C++ you can change temporaries ... if they are of class type! You can call non-const member functions on a temporary. This is quite similar to binding a temporary to a non-const reference and changing it. Section 3.10.10 in C++ ISO/IEC 14882:1998 standard clearly mentions this exception. There are at least two practical use of such an exception. One is the " Named Parameter " idiom and the other one is the Move Constructor idiom . In case of the named parameter idiom, the member functions might prefer to return the object by no

LEESA: A new way of typed XML programming in C++

Some of my recent research work has focused on developing a highly generic and reusable library for complex object structure traversal, which is best exemplified by schema driven XML programming. I'm glad to present a research paper called LEESA: Embedding Strategic and XPath-like Object Structure Traversals in C++ , which will be published in the proceedings of IFIP Working Conference on Domain Specific Languages (DSL WC) , 2009 at Oxford, UK. LEESA stands for L anguage for E mbedded qu E ry and traver SA l. LEESA has advanced the state-of-the-art of the typed XML programming in standard C++ to a level where many benefits of static type analysis can be maintained while enjoying a succinct syntax similar to that of XPath. Below, a quick motivating example of LEESA that sorts and prints the names of the authors in a XML book catalog is shown. Catalog() >> Book() >> Author() >> Sort(Author(), LastNameComparator) >> ForEach(Author(), print); The key thing t