Writing const-correct code in D

[Kevin Bealer]

Also, this is not full "C++ const", only parameter passing and const
methods, which seems to be the most popular parts of the const idea.
It seems like it should require more syntax that C++, but it only
takes a small amount.


When working with types like "int", use "in" - const is not too much
of an issue here.

The same is true for struct, it gets copied in, which is fine for
small structs.  For larger structs, you might want to pass by "in *",
i.e. use "in Foo *".  You can modify this technique to use struct, for
that see the last item in the numbered list at the end.


For classes, the issue is that the pointer will not be modified with
the "in" convention, but the values in the class may be.

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