That is exactly how it should behave, because the left-side value may
not be valid, and the is operator is meant to help confirm that.
In the meantime, I've updated your patch to work with the current trunk:
https://bugs.freepascal.org/view.php?id=33603#c117040
Gareth aka. Kit
On 02/07/2019 21:31, Ondrej Pokorny wrote:
On 02.07.2019 21:48, J. Gareth Moreton wrote:
I should probably test this myself, but if you, say, read a value
from a file directly into a variable of type TEnumType, will your
patch return False for "if (Value is TEnumType) then" if Value,
despite being TEnumType, contains an invalid value? No problem if it
isn't, just that you would have to read an Integer-type first then
typecast it.
Yes:
var
Value: TEnumType;
begin
Value := TEnumType(-1);
IsValid := Value is TEnumType; // IsValid gains false
The compiler may not do any optimizations here (like return always
true if the left side value is the enum type at the right side). This
should be clearly stated and documented if the feature is added to FPC.
This is similar to the object-is operator that gets evaluated as well
even if the type of the left-side value is the type at right side:
var
Value: TPersistent;
begin
Value := TPersistent(TObject.Create);
IsValid := Value is TPersistent; // IsValid gains false
Ondrej
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