[fpc-pascal] User-defined operators and dummy parameters
Is it possible to pass a dummy parameter to a user-defined operator,
with no expectation that it be referenced?
The following test program compiles OK but fails at runtime with an
error 217 on all platforms if the record is empty. It works if it
contains a variant, but not reliably with other types.
program test;
{$mode objfpc}{$H+}
typet1= array of integer;
r_= record
// x: variant
end;
var a1: t1;
reduce: r_ = ();
procedure print(const a: t1);
var i: integer;
begin
for i := Low(a) to High(a) do
Write(a[i], ' ');
WriteLn
end { print } ;
operator + (const r: r_; const a: t1) s: variant;
var i: integer;
begin
s := 0;
for i := Low(a) to High(a) do
s += a[i]
end { + } ;
begin
// a1 := t1([1,2,3,4,5]); Doesn't work without tuple support
SetLength(a1, 5);
a1[0] := 1;
a1[1] := 2;
a1[2] := 3;
a1[3] := 4;
a1[4] := 5;
WriteLn('a1:');
print(a1);
WriteLn('+/ a1:');
WriteLn(reduce + a1);
WriteLn
end.
This is of no particular importance, I'm just exploring capabilities.
--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk
[Opinions above are the author's, not those of his employers or colleagues]
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[fpc-pascal] Re: User-defined operators and dummy parameters
works if I change the operator header to: operator + (const r: r_; const a: t1) s: integer; from gdb bt, the problem seems to be assignment from shortint to variant: #0 0x in ?? () #1 0x08057205 in SYSTEM_$$_assign$SHORTINT$$VARIANT () #2 0x0806bf94 in U_$SYSTEM_$$_OUTPUT () #3 0x0804816f in plus (R=..., A=0xb7ff7068) at x.pas:30 #4 0x080482ef in main () at x.pas:47 > Doesn't work without tuple support a1 := t1.create(1,2,3,4,5); -- View this message in context: http://free-pascal-general.1045716.n5.nabble.com/User-defined-operators-and-dummy-parameters-tp5716106p5716107.html Sent from the Free Pascal - General mailing list archive at Nabble.com. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Re: User-defined operators and dummy parameters
leledumbo wrote: works if I change the operator header to: operator + (const r: r_; const a: t1) s: integer; from gdb bt, the problem seems to be assignment from shortint to variant: #0 0x in ?? () #1 0x08057205 in SYSTEM_$$_assign$SHORTINT$$VARIANT () #2 0x0806bf94 in U_$SYSTEM_$$_OUTPUT () #3 0x0804816f in plus (R=..., A=0xb7ff7068) at x.pas:30 #4 0x080482ef in main () at x.pas:47 [Digs] Thanks, you're right :-) Also, if the array elements are variants then there's no error. So in other words, it might turn out to be safer to have separate operators returning integer, double and so on. I appreciate that I'm abusing the language here, but /should/ the original implicit conversion have worked? Doesn't work without tuple support a1 := t1.create(1,2,3,4,5); Noted. What happens in this case if a1 := t1.create(1,2,3,4,5); .. a1 := t1.create(6,7,8,9); Does there have to be an explicit destroy or similar? -- Mark Morgan Lloyd markMLl .AT. telemetry.co .DOT. uk [Opinions above are the author's, not those of his employers or colleagues] ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
[fpc-pascal] Re: User-defined operators and dummy parameters
> I appreciate that I'm abusing the language here, but /should/ the original implicit conversion have worked? I don't know, but IMO it should. Well, a variant should be able to accept any variant compatible type, right? > Does there have to be an explicit destroy or similar? Nope, dynamic arrays are reference counted. When you re-assign the variable with a new array, reference count of the previous array reaches 0 and thus automatically freed. -- View this message in context: http://free-pascal-general.1045716.n5.nabble.com/User-defined-operators-and-dummy-parameters-tp5716106p5716109.html Sent from the Free Pascal - General mailing list archive at Nabble.com. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
[fpc-pascal] When does a reference counted object get freed automatically, and when not?
I've been exploring interfaces a bit, and fail to understand when
automatic destruction of an object is precipitated by the compiler, and
when not.
Consider the lifetime of the two instances i1 and i2 in the following
program. It seems that i2 (called in a method of i1) is freed
automatically, but i1 is not.
== code begin ==
program integerInterface;
{$mode objfpc}{$H+}
type
ISortableInteger = interface
['{D38A748E-F889-4A2A-9E3C-5154D493061C}']
function Compare(anIntf: ISortableInteger): integer;
procedure SetValue(aValue: int64);
function GetValue: int64;
property Value: int64 read GetValue write SetValue;
end;
{ TSortableInteger }
TSortableInteger = class(TInterfacedObject, ISortableInteger)
strict private
Fint: int64;
procedure SetValue(aValue: int64);
function GetValue: int64;
public
function Compare(anIntf: ISortableInteger): integer;
property Value: int64 read GetValue write SetValue;
end;
{ TSortableInteger }
function TSortableInteger.Compare(anIntf: ISortableInteger): integer;
begin
if Fint > anIntf.Value then
Result := 1
else if Fint = anIntf.Value then
Result := 0
else
Result := -1;
end;
function TSortableInteger.GetValue: int64;
begin
Result := Fint;
end;
procedure TSortableInteger.SetValue(aValue: int64);
begin
Fint := aValue;
end;
var i1, i2: TSortableInteger;
begin
i1 := TSortableInteger.Create;
i1.Value := 21;
i2 := TSortableInteger.Create;
i2.Value := 22;
WriteLn('i1 (21) compared to i2 (22) is ',i1.Compare(i2));
i1.Free; // why is this necessary with a reference counted interface?
ReadLn;
end.
== code end ==
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Re: [fpc-pascal] When does a reference counted object get freed automatically, and when not?
In our previous episode, Howard Page-Clark said: > > var i1, i2: TSortableInteger; _INTERFACES_ are refcounted, not classes. And these are class references. Change it to ISortableInteger, remove the free, and it will work fine probably. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
