Programming

Why use interface instead of pimpl

The opaque pointer (pimpl) idiom has been inherited from C language where it is used to encapsulate implementation details. However, both old-school and "modern" C++ dispence you from writing some ugly code, and allow to use interfaces with object factories.

The example of implementation with both pimpl and interface approach is as follows.

All expressions of 123456789 and signs +/- which value is 100

Suppose a string of ordered cyphers 123456789. You can insert signs "+" and "-" between any cyphers to make a correct arithmetical expression. The problem is to find all expressions which sum is 100.

This problem may be interesting for dynamic script languages having the function of a string expression evaluation.

E.g. solving in bash

static_cast vs dynamic_cast: undefined behavior

Do not use static_cast when you cast from a basic class to a derived one. This may lead to undefined behavior. To handle the polymorphism, a virtual inheritance or a multiple inheritance case always use dynamic_cast instead.

The following short example shows the undefined behavior cases. This works with GCC, VC and online C++ shells:

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