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Free Pascal => Beginners => Topic started by: Anonimista on September 11, 2019, 08:53:44 pm

Title: Why is an enumeration out of range error not cought compile time
Post by: Anonimista on September 11, 2019, 08:53:44 pm

I have this code:

Code: Pascal  [Select][+][-]

1. program project1;
2.  
3. type
4.     shape = (rectangle, square, ellipse, circle);
5.     color = (red, yellow, green);
6.     sex = (male, female);
7.  
8. var
9.     s: sex;
10.     c: color;
11.  
12.  
13. begin
14.  
15.     s := male;
16.     writeln(s);
17.     writeln(succ(s));
18.     { writeln(pred(s)); -- Runtime error 107 }
19.     writeln(ord(pred(s)));
20.  
21.     c := red;
22.     writeln(c);
23.     writeln(succ(c));
24.  
25.     readln;
26.  
27. end.

The error is "Invalid enumeration
    Reported when a text representation of an enumerated constant cannot be created in a call to str or write(ln)."

Can anybody explain why this error is not caught at compile time. Is it to keep the compiler simple?

Title: Re: Why is an enumeration out of range error not cought compile time
Post by: jamie on September 11, 2019, 09:15:11 pm

Delphi help says not to use a PRED on a WRITE operation because WRITE does not have a way to translate it to something usable.


 In your example, you are actually faulting it because you are going outside the boundaries.

Title: Re: Why is an enumeration out of range error not cought compile time
Post by: Anonimista on September 11, 2019, 09:22:07 pm

hm, I only get the error when ord(s) is -1. I guess my question is why are enumeration bounds not checked at compile time.

Title: Re: Why is an enumeration out of range error not cought compile time
Post by: marcov on September 11, 2019, 09:22:52 pm

I think pred(s) and succ(s) are simply not inlined as intrinsics in this code. Then the increment/decrement doesn't happen in compiletime, so no error.

Title: Re: Why is an enumeration out of range error not cought compile time
Post by: Anonimista on September 11, 2019, 09:43:29 pm

Thanks! New to freepascal and not quite understand much but it is what it is.