C++ for Scientists - Technische Universität Dresden
C++ for Scientists - Technische Universität Dresden
C++ for Scientists - Technische Universität Dresden
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7.5. FROM MONOMORPHIC TO POLYMORPHIC BEHAVIOR 219<br />
• Static type checking: All types are checked statically.<br />
• Static binding (prevents separate compilation):All types are bound statically.<br />
• Efficiency: Compile-time evaluation and static binding allow optimization and efficiencies<br />
not available with dynamic binding.<br />
7.5.3 Comparison of Static and Dynamic Polymorphism<br />
Here the main features from static and dynamic polymorphism are summarized:<br />
• Virtual function calls are slower during run time than function templates: A virtual<br />
function call includes an extra pointer dereference to find the appropriate method in the<br />
virtual table. By itself, this overhead may not be significant. Significant slowdowns can<br />
result in compiled code because the indirection may prevent an optimizing compiler from<br />
inlining the function and from applying subsequent optimizations to the surrounding code<br />
after inlining.<br />
• Run time dispatch versus compile-time dispatch: The run time dispatch of virtual functions<br />
and inheritance is certainly one of the best features of object-oriented programming.<br />
For certain kinds of components, run time dispatching is an absolute requirement, decisions<br />
need to be made based on in<strong>for</strong>mation that is only available at run time. When this<br />
is the case, virtual functions and inheritance are needed.<br />
Templates do not offer run time dispatching, but they do offer significant flexibility at<br />
compile time. In fact, if the dispatching can be per<strong>for</strong>med at compile time, templates offer<br />
more flexibility than inheritance because they do not require the template arguments types<br />
to inherit from some base class.<br />
• Code size: virtual functions are small, templates are big:: A common concern in templatebased<br />
programs is code bloat, which typically results from naive use of templates. Carefully<br />
designed template components need not result in significantly larger executable size<br />
than their inheritance-based counterparts.<br />
• The binary method problem: There is a serious problem that shows up when using inheritance<br />
and virtual functions to express operations that work on two or more objects.
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