Saturday, October 3, 2009

iterators - what go into "<>" and "()"

motivation -- i find declarations too complicated when iterators are involved.

* in a template definition's < >, people put iterator categories like InputIterator. I think these are just suggestive dummy typenames. If you rename to "input_iterator" through out that class, nothing will break. In fact, when you write template < class Animal>, Animal cannot be a real class name.

* in function prototypes, you use those fake types declared earlier. See [[essential c++]]
* in concrete function calls, you feed in variables representing iterators. You need to follow the suggestions in the iterator category. Otherwise, things break, though Compiler can't detect, i think.

Now let's extend the question
Q2: what do u put into < > vs () for a function template [1] using iterators?
[1] such as those STL algorithms

A: i think iterator is an atypical example. See [[java interface as a replacement for c++ templates]] for background.
* in prototypes' < > you can put anything silly like T, S, V
* in prototypes' (), you can use those same type param, or a ptr/ref to it. An iterator argument can be derived from these fake types or standalone.
* in concrete function calls, you can feed a specific iterator type into < >, and arguments into (). Usually you can omit the < > stuff because compiler can infer.

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