[C++] Automatically determine size of arrays

[frank-aurich]

When creating objects that contain array members, we currently have to explicitly set the number of elements in the array, even though the count is implictly available internally.

struct Line
{
   varsize numPositions : numPositions > 0;
   Position pn[numPositions];
}

The generated C++ code for the above object allows us to write something like this:

BitStreamWriter bsw;
Line line;
line.setPn({Position(20, 50)});
line.write(bsw);

This compiles just fine, but will throw an exception at runtime, because numPositions was not explicitly set.

Instead we have to write:

BitStreamWriter bsw;
Line line;
line.setPn({Position(20, 50)});
line.setNumPositions(1);
line.write(bsw);

This is cumbersome and error-prone. Since the Line object in C++ internally holds pn as an std::vector, the element count is implicitly available and should be deduced when writing the object.

[mikir]

We could think about this but only for such trivial array size expressions. Unfortunately, we are not able to find out any generic solution for that. Consider the following schema:

struct Line
{
   varsize numPositionsA : numPositionsA > 0;
   varsize numPositionsB : numPositionsB > 0;
   Position pn[numPositionsA + numPositionsB];
}

Now, we are not able to deduce from size of pn array what is numPositionsA and what is numPositionsB.

[mikir]

This is a duplicate of #556.