C++ for Scientists - Technische Universität Dresden

Effective Programming: The
Polymorphic Way
Chapter 7
Fools ignore complexity. Pragmatists suffer it. Some can avoid it. Geniuses remove
it.
—Alan Perlis
To remove complexity in scientific application development (but not only there), several programming
techniques, methods, and application of paradigms have to be used accordingly. This
not only depends on the ability to combine application-specific functionality with other librarycode
from a variety of sources but also to restrict the amount of application-specific glue code.
So libraries must remain open for extension but closed for modification, which can be attributed
to a technique called polymorphic programming.
The presented sections of this book introduced important mechanisms to successfully develop
scientific applications such as C++ basics, encapsulation, generic and meta programming as
well as inheritance. An important part of scientific computing, matrix containers and matrix
algorithms, has been presented to aid the topics so far. Effective programming is then possible if
these mechanisms are not viewed as separate entities, but as different characteristics to achieve
important goals, such as
• uncompromising efficiency of simple basic operations (e.g., array subscripting should not
incur the cost of a function call),
• type-safety (e.g., an object from a container should be usable without explicit or implicit
type conversion),
• code reuse and extensibility,
all with their respective advantages and disadvantages. This section reviews important techniques
to achieve polymorphism from a more general point of view and highlights a basic but
very important recurring principle for scientific computing: code reusability. This is not mainly
because programmers are lazy people, but also because applications have to be tested. For
the field of scientific applications this is particularlly important due to large parameter sets,
changing boundary and initial conditions, as well as long run-times of simulation codes. Hence
it should not be underestimated how much time and effort can be saved, if already tested code
can be used as starting point or reference. So code reusability is not only about programming
less, but also because of extend code quality. Most of the presented and discussed technique so
199