[fpc-devel] Debug compiler

Jonas Maebe jonas.maebe at elis.ugent.be
Sun Nov 1 16:38:18 CET 2015

On 01/11/15 06:26, Ondrej Pokorny wrote:
> On 01.11.2015 00:11, Jonas Maebe wrote:
>> On 31/10/15 21:28, Ondrej Pokorny wrote:
>>> The argument that the tenumeratornode concept is completely different
>>> from other nodes is correct - but if you think about the syntax you will
>>> see that also the syntax is completely different from other pascal
>>> syntax so you need such a unique node.
>> That is a very good argument not to add it...
> Yes, my argument that the "syntax is completely different from other
> pascal syntax" is misleading. I put it wrong. It is not different - its
> a new extension within the current pascal syntax:

The basic issue is that you need extra context for supporting this 
extension. Normally, an enumerator is searched based on the class type. 
In your case, it's searched either based on the class type, or if the 
class is returned from a property with an "enumerator" specifier, based 
on that enumerator declaration.

Whether you do it via a temporary node, a global variable and/or node 
flags, does not change that. Extra context is always bad both for the 
compiler implementation/maintenance and for code 
readability/predictability by humans.

This leads to more design design decisions:
1) do you a) forbid an enumerator specification if the class already has 
an enumerator, b) hide the existing enumerator, or c) allow enumerating 
both via the property and the original class enumerator? If you all 
both, how do you differentiate? If b), first assigning the property to a 
variable and iterating over that will have a different result than 
directly iterating over the property, which is bad for understandability 
and code predictability. If c), how do you specify it. If a), that break 
orthogonality (and I'm sure some people will argue that iterating over a 
particular property may have to be done differently than over that 
class' contents in the general case)

2) do you expose the "hidden/parent" enumerator of the class itself to 
the overriding enumerator in a property and if so, how? Maybe even 
iterating both at the same time via some kind of inheritance mechanism?

There are undoubtedly more.


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