On 27/01/18 16:28, Jonas Maebe wrote:
Jonas Maebe wrote:
C Western wrote:
The following innocuous looking code generates a range check error:
{$R+}
function Count: qword;
begin
Result := 0;
end;
var
i: Integer;
begin
for i := 0 to Count-1 do
WriteLn(i);
end.
I can (more or less) see why
I changed the type used to evaluate for-loop bounds in ISO Pascal mode
because of https://bugs.freepascal.org/view.php?id=24318 . Maybe the
same should be done for other non-TP/Delphi modes too.
Actually, it won't help because "qword - 1" will still be evaluated as
qword. The issue is that there is no safe way to evaluate this with
range checking that is correct in all cases without a 128 bit integer type:
1) if you evaluate it as qword, you get a range error if count is 0 (as
above)
2) if you evaluate it as int64, then if count is high(int64)+1 you will
get a range error even though the result could be represented in int64
In this particular case, because the counter is 32 bit (which seems
quite unsafe for use with a container whose "count" property is 64 bit),
using int64 would be "correct", but it's not a systemic solution (as
shown above) and hence not something to implement in the language.
The actual code that triggered my interest was:
procedure LCLViewExtension.lclSetEnabled(AEnabled: Boolean);
var
ns : NSArray;
i : integer;
obj : NSObject;
begin
ns := subviews;
for i := 0 to ns.count - 1 do
begin
obj := NSObject(ns.objectAtIndex( i ));
... process obj ...
end;
end;
I suppose i should be declared as the same type as ns.count which is
NSUInteger = qword, but this will still trigger the error. You can avoid
the problem by coding the loop as:
for i := 1 to ns.count do
begin
obj := NSObject(ns.objectAtIndex( i-1 ));
so I suppose the real flaw is that the first item is at index 0, rather
than 1, but I don't think that is a battle I am going to win.
Given how common the above bit of code is likely to be, I can't see any
way of fixing this without some work in the compiler.
Colin
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