Glulx "system constants" not usable like number constants in defining arrays?

I was trying to set up a table arary that would vary in size based on the number of objects. In Glulx, there is a “system constant” (name given in Inform 6.34 release notes) called #highest_object_number that is defined during compilation, which would hold the value that I want, but the declaration:

Constant ObjectCount = #highest_object_number;
Array ObjectData table (ObjectCount*2);

is being rejected ("Error: Expected constant but found "). Based on the error, I’m assuming that the compiler is deciding that the value of #highest_object_number is being treated like a variable, not a constant. A declaration using a “hard-coded” constant:

Constant ObjectCount = 10;
Array ObjectData table (ObjectCount*2);

is accepted.

Should system constants be accepted for this type of usage? If not, what’s the reasoning behind disallowing it?

The values of the system constants are not known until all of the source code has been compiled. Your example uses #highest_object_number; obviously it doesn’t make sense for this to have a value until all the objects have been created. All arrays, objects, strings, and functions must also be created and laid out in memory.

There is a following step where values (in function code) can be filled in with system constants. For example, you could have a function

[ func x;
    x = #highest_object_number;

Filling in that value does not change the layout of memory. But it doesn’t make sense to fill in an array length that way.

If you really want an array with the size of one of these constants you could create it with malloc in an initialisation function.

@zarf, I did understand that it was a number that had to be discovered during compilation, but it seems like the compiler is able to decide what that number is by that point in the code generation – after all, the constant ObjectCount is set correctly.

That’s why I had thought that by putting that value into a constant, the compiler would have determined it prior to creating the code for the array declaration. But it just doesn’t work that way, it seems? (I’m afraid that I don’t know much about how compilers work on the inside.)

I had also hoped that those values being called system constants meant that they should be treatable as such. Oh, well – now I know that they’re not, so thank you.

@Dannii, thank you for the tip. I will look into that approach!

ObjectCount is not in fact set until that last step of filling in constant values. Before that, it’s a placeholder which says “fill in #highest_object_number here.”