El 16/07/2018 a las 21:27, Marco van de Voort escribió:
In our previous episode, Sven Barth via fpc-pascal said:
function)
In such cases, you don't declare it "auto". Just as you don't free a
pointer in the function you declare it if you pass the instance to another
code that stores it beyond the life time of the function
But you don't necessarily know that the function you call does that (think
third party code). And people *will* use this and don't think about the
consequences. So a system with automatic reference counting is safer and
that is what is planned, if at all.
Moreover the use case, dynamically instantiated classes with very local
scope is rare.
You must be kidding. You use local scope objects everywhere. The
TStreams family is a clear example.
source/rtl/objpas/classes/classes.inc
//----------------------------------------
function CollectionsEqual(C1, C2: TCollection; Owner1, Owner2:
TComponent): Boolean;
procedure stream_collection(s : tstream;c : tcollection;o : tcomponent);
var
w : twriter;
begin
w:=twriter.create(s,4096);
try
w.root:=o;
w.flookuproot:=o;
w.writecollection(c);
finally
w.free;
end;
end;
var
s1,s2 : tmemorystream;
begin
result:=false;
if (c1.classtype<>c2.classtype) or
(c1.count<>c2.count) then
exit;
if c1.count = 0 then
begin
result:= true;
exit;
end;
s1:=tmemorystream.create;
try
s2:=tmemorystream.create;
try
stream_collection(s1,c1,owner1);
stream_collection(s2,c2,owner2);
result:=(s1.size=s2.size) and
(CompareChar(s1.memory^,s2.memory^,s1.size)=0);
finally
s2.free;
end;
finally
s1.free;
end;
end;
//----------------------------------------
// auto version
//----------------------------------------
function CollectionsEqual(C1, C2: TCollection; Owner1, Owner2:
TComponent): Boolean;
procedure stream_collection(s : tstream;c : tcollection;o : tcomponent);
var
w : twriter;auto;
begin
w:=twriter.create(s,4096);
w.flookuproot:=o;
w.writecollection(c);
end;
var
s1,s2 : tmemorystream; auto;
begin
result:=false;
if (c1.classtype<>c2.classtype) or
(c1.count<>c2.count) then
exit;
if c1.count = 0 then
begin
result:= true;
exit;
end;
s1:=tmemorystream.create;
s2:=tmemorystream.create;
stream_collection(s1,c1,owner1);
stream_collection(s2,c2,owner2);
result:=(s1.size=s2.size) and
(CompareChar(s1.memory^,s2.memory^,s1.size)=0);
end;
//----------------------------------------
With "Auto", you save a lot of "try finally free" that add nothing to
algorithm
You can argue against "auto" in the grounds of "Aesthetic symmetry ",
"it's not explicitness pascal way", "it's not worth", "confusion mixing
styles/paradigms" or other arguments I haven't thought. I asked
expecting those arguments I hadn't thought about.
There may be valid arguments against, but when I read "local scope for
classes is rare", I know I am in the grounds of a irrational
resistance. In such cases, a "For the sake of brevity, my vote is
simply "no" to all your suggestions." is the best answer.
--
Saludos
Santiago A.
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