[fpc-pascal] Set size limit

[Mark Morgan Lloyd]

Daniel Gaspary wrote:
> On Mon, Mar 11, 2013 at 7:09 AM, Mark Morgan Lloyd
> <markMLl.fpc-pascal at telemetry.co.uk> wrote:
>> That was pretty much my gist. Since these days Unicode is larger than 65536
>> codepoints I don't think there's any advantage to expanding sets from 256 to
>> 65536 elements, efficient operations on sparse arrays of 256-element sets
>> would be far better.
> 
> In my case the enum has near 600 elements.
> 
> TMyEnum = (me1, me2...);
> 
> The set though would never be used to contain more than 256.
> 
> TMySet = set of TMyEnum;
> 
> Is it not viable to modify the compiler to compile the code and raise
> an exception if I try to add more than 256 elements to the set ?

No, because the elements in a set are dictated by their position. A set 
that can contain anything between 0 and 256 elements occupies 8 bytes in 
memory with the (bit representing the) 0 element at one end and the (bit 
representing the) 256 element at the other, a set to contain up to (say) 
257 elements would require more space and that's not supported.

-- 
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk

[Opinions above are the author's, not those of his employers or colleagues]