On Thu, 28 Jul 2016, Maciej Izak wrote:
2016-07-28 16:37 GMT+02:00 Michael Van Canneyt <mich...@freepascal.org>:
Are there additional benefits I have missed ?
Using nilable (I think nilable is better than nullable) records is terrible
without default field:
=== code begin ===
var
n: TNilable<TRec>;
x: TRec;
begin
{
... let say that n is assigned somewhere, assume that n.HasValue = true
}
// to change any field in nilable n you need to...
x := n.Value;
OK, you convinced me for this one :-)
Michael.
that will change nothing, just look below. Just harder to usage pure
non-pascalish clone of C# struct (finally C# has pointers as
nonstandard/unsafe type so feature with direct dereference is disabled by
design).
=== code begin ===
procedure SomeTest(x : Integer);
begin
end;
Var
A : TNullable<Integer>;
begin
SomeTest(A.Value); // AV error here!
end.
=== code end ====
A^ is shortcut for A.Value but has advantage = direct dereference to
Instance.
Here I am not convinced.
This is an artifact of your implementation: you use a pointer.
There is no need to use a pointer. One can just as well do
TNullable <T> = Record
Private
Fvalue : T;
IsNotNull : Boolean;
Public
// all the rest, including
Property Value : T Read GetValue Write SetValue;
Property IsNull : Boolean Read GetIsNull;
end;
Then you will not have this problem;
GetValue will always return a 'Default' value.
Michael.
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