cpptod: add function input and output parameters.

[carun]

First attempt to renew PR #1840.

I respect and appreciate the work of the original author. However I think that this PR explains a trivial difference between C++ and D. Please consider if this is really required to be merged.

C++ to D article ought to contain the important differences that eases the transition of a C++ programmer (from his preconceived notions) to D. It should be packed with information. Trivial topics could dilute the focus of this article. Things like struct, RAII, are good places for improvement, I believe.

Just my 2 cents.

[dlang-bot]

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[carun]

I think that this PR needs to be even more accurate.

C++ has only const and volatile (which is a different subject) as qualifiers for function parameters. D improves over C++ by introducing many new qualifiers to the function parameters (in, out, const, immutable, inout, ref and many more, but I'm stating those that are applicable for programmers transitioning from C++) that lets the reader clearly infer what the function does by just look at it's signature. We don't even have to explain what void getArea(in int width, in int height, out int area); does (without even knowing the pass by reference semantics). The function signature is self explanatory.

Both C++ and D support input and output parameters. C++ supports it in the form of pass-by-reference (and pointer). In addition, D improves over C++ by differentiating between value types and reference types and also though the function parameter qualifiers. So in my opinion this PR needs a complete rewrite.