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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