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Why is an enumeration out of range error not cought compile time
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Topic: Why is an enumeration out of range error not cought compile time (Read 979 times)
Anonimista
New Member
Posts: 19
Why is an enumeration out of range error not cought compile time
«
on:
September 11, 2019, 08:53:44 pm »
I have this code:
Code: Pascal
[Select]
[+]
[-]
program
project1
;
type
shape
=
(
rectangle
,
square
,
ellipse
,
circle
)
;
color
=
(
red
,
yellow
,
green
)
;
sex
=
(
male
,
female
)
;
var
s
:
sex
;
c
:
color
;
begin
s
:
=
male
;
writeln
(
s
)
;
writeln
(
succ
(
s
)
)
;
{ writeln(pred(s)); -- Runtime error 107 }
writeln
(
ord
(
pred
(
s
)
)
)
;
c
:
=
red
;
writeln
(
c
)
;
writeln
(
succ
(
c
)
)
;
readln
;
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?
Logged
jamie
Hero Member
Posts: 6131
Re: Why is an enumeration out of range error not cought compile time
«
Reply #1 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.
«
Last Edit: September 11, 2019, 09:18:00 pm by jamie
»
Logged
The only true wisdom is knowing you know nothing
Anonimista
New Member
Posts: 19
Re: Why is an enumeration out of range error not cought compile time
«
Reply #2 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.
Logged
marcov
Administrator
Hero Member
Posts: 11458
FPC developer.
Re: Why is an enumeration out of range error not cought compile time
«
Reply #3 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.
Logged
Anonimista
New Member
Posts: 19
Re: Why is an enumeration out of range error not cought compile time
«
Reply #4 on:
September 11, 2019, 09:43:29 pm »
Thanks! New to freepascal and not quite understand much but it is what it is.
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Why is an enumeration out of range error not cought compile time
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