[fpc-pascal] Optional param modifier

Ryan Joseph ryan at thealchemistguild.com
Mon Apr 15 00:53:31 CEST 2019

> On Apr 14, 2019, at 6:30 PM, Martin Frb <lazarus at mfriebe.de> wrote:
> I would actually argue that it is infinitely more important to check for nil after MakeThing. (Unless I know for sure it is not needed: proof, docs)
> Assuming (taking the danger of doing so) both do what there name indicates, then:
> - If I forget to check after FindThing, it is likely to cause an error very soon, and most probably while I am testing myself.
> - If I forget it after MakeThing, it may be very rare to cause an error. It will likely pass my tests, and cause a customer of mine some stress.

I understand all your concerns over not wanting to use this so I would suggest to avoid it (we all feel that way about certain features). Since no-one thinks this is a good idea I’ll forget about because it’s not that important anyways. Waiting for nullable types is maybe a better option anyways and those are in the pipeline via default properties. 

What Sven brought up is more immediately useful anyways and I can think of many times I have the mandatory top part of the function that checks to make sure parameters are valid. Formalizing this process would be a smart thing I think. If you don’t agree, then don’t use it. ;)

That’s what I read from the link posted. As for the “ensure” block now that I don’t see as a pattern that I can recognize. Any real world examples of this? 

Here’s what I imagine that would look like:

procedure CreateHero (name: string; hp: integer);
  name <> '';
  (hp > 0) and (hp < 100); 
  // compilers parses the conditions and inserts as if statements:
  // if name <> ‘’ then
  //   assert(‘condition "name <> ‘'" for CreateHero failed’);
  // if (hp > 0) and (hp < 100) then
  //   assert(‘condition "(hp > 0) and (hp < 100)" for CreateHero failed);

Pretty simple right?

	Ryan Joseph

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