Paul Ishenin pisze:
Of course. for-in loop expect to have a collection not an enumerator.
What enumerator should for-in loop to choose in the next case:
[example]
TMyListEnumerator = class
public
function GetEnumerator: TMyListEnumeratorEnumerator;
function MoveNext: Boolean;
property Current: something;
end;
TMyList = class
public
function GetEnumerator: TMyListEnumerator;
function GetAnotherEnumerator: TMyListAnotherEnumerator;
end;
var
List: TMyList;
begin
for i in List.GetEnumerator do
end;
[/example]
Loop will choose TMyListEnumeratorEnumerator, but is it desired?
'using' keyword solves this ambiguity very easy:
for CollectionElement in Collection using CollectionEnumerator do
with hack with trivial operator we receive the same:
for CollectionElement in Collection.CollectionEnumerator do
but what about
for CollectionElement in Collection using TreeEnumerator do
where TreeEnumerator cant traverse thought Collection
And second: You cant pass enumerator as param.
Maybe you understood me wrong? I proposed the 'using' keyword as an
extension to the current implementation. It would not be required.
If not used then it will work as now but if used then compiler will
search for the given identifier and use it instead of
operator/GetEnumerator method.
this is third method,
Should be good point to implement this (pascal always has very simple
semantic and very strong type checking)
Of course you then you can use any enumerator with any collection,
but it will be better?
How many errors we then invoke?
Much less.
I can't resist.
But I have another proposition. Because we add so many variants to forin
construction, can be added once more.
[example]
for list do ....
[/example]
where we omit in keywords and iteration variable
That will be nice solution for some expression or in some transactional
patterns like:
[example]
initfun;
while stopfun do begin
end;
try
lock;
...
finally
unlock;
end;
[example]
I think its not break any current behavior. Of course I can do the same
today, but I need variable, which would not be used.
In below example we can omit declaration of i variable;
[example]
var
i : integer;
begin
for i in lock do begin
procedureNotUseI;
end;
end;
[/example]
--
Darek
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