On 20/09/2011 13:21, Skybuck Flying wrote:
The problem with properties currently is that it does not allow partial
modification of records or arrays, when a property is of type record or
array it's a everything or nothing situation, either the entire
record/array
is overwritten/returned or nothing at all, this is very inconvenient and
also bad for performance.
This is not the prolem with properties. This is what "property" means in
pascal. This is the reason why there is a property at all.
If you don't want that, do not use a property, just use a field
(member/variable) instead.
you can always do
TFoo =Class
public
Bar: TSomeRecord; // field/variable
end;
And all will work.
The main reason to use a property
property Bar: TSomeRecord read Fbar write FBar
is to declare that the implementer reserves the right, to later put
getter/setter function/procedures in place
It tells the compiler, that while the developer did not yet write any
such code, the compiler should/must protect "Bar" in a way that any code
referring to it, will work, if getter/setters are written.
But with a getter, Bar is a function result => so you can not do
GetBar().xyz := 1
At least not meaningful: because you do not have the original FBar, you
only have a temporary copy returned by GetBar.
Even if pascal would have functions that return lvalues, GetBar could
have created a result on the fly. There may not be a FBar variable at all.
function GetBar: TSomeRecord;
begin
Result.xyz := random(5);
end;
With this function, what you suppose that "Bar.xyz := 1;" should do?
Since Bar is GetBar, which retturns a record created on the fly, that
will be dropped straight away
The only way ossible would be for the compiler to translate it into
tmp := Bar; tmp.xyz := 1; Bar:=tmp;
which would be the same as
tmp := GetBar(); tmp.xyz := 1; SetBar(tmp);
And SetBar could have plenty of side effects, that do far more than just
updating xyz.The original code never said to update the entire "Bar" =>
so it must not be translated to do so.
So again: using the keyword property means =>assume there is no variable
at all; assume it may be a function, getter/setter ....
If you do not want that, do not use it.
There is no rule, that you must use properties. Making a field public
accessible is absolutely ok.
Most peopl edo not do it => because, if uou do not have a specific
reason to do it, then using property means that at absolutely no cost,
you can reserve the possibility of future extension should you need to.
Hence, unless you have a good reason not to use property, you should use
it. But if your design does not allow for it, do not use it.
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