topic Re: Deleting Objects in v15 in Discussions

Deleting Objects in v15

David_Burnham — Mon, 18 Nov 2019 19:03:32 GMT

In JSL I can define a class and use it as a template to instantiate objects.

How do I delete the object?

I've been using the message deleteClass, assuming its a slight misnomer and really it's deleting the object.

But in version 15 it really does seem to delete the class. Once I use the message I'm unable to create any further instances of the class.

I can use a delete message but I think its just an alias for deleteClass and I have the same problem.

Is delete class really intended to wipe out the entire class definition? If so, what is the correct way of deleting the object?

Here is a simple test script:

names default to here(1);

defineClass("MyClass",{
	_value = .,
	_init_ = method({value},
		_value = value;
	),
	getValue = method({},
		return(_value)
	)
});

// this works
obj = newObject( MyClass( 10 ) );
show(obj:getvalue);

// this works 
obj = newObject( MyClass( 20 ) );
show(obj:getvalue);

// there should be no harm deleting
// an object once I am finished with it
obj<<delete;

// but this now fails ...
obj = newObject( MyClass( 30 ) );
show(obj:getvalue);

Re: Deleting Objects in v15

pmroz — Mon, 18 Nov 2019 20:24:36 GMT

Does this work: obj = .;

Re: Deleting Objects in v15

David_Burnham — Mon, 18 Nov 2019 20:37:40 GMT

I don't know.

Before it was possible to "define classes" I created them using namespaces.

For namespaces this doesn't work i.e. setting the variable to missing is not the same as deleting the namespace.

ns = newNamespace("xyz");
ns:a = 10;

ns = .;

show namespaces();

Re: Deleting Objects in v15

Craige_Hales — Tue, 19 Nov 2019 01:01:44 GMT

I don't understand how to use it either. I think you don't need it:

Define Class(
	"aa",
	{_init_ = Method( {a}, this:b = a ), //
	x=1, //
	m1 = Method( {a, b}, a * b )}
);

// 
lcaa42 = New Object( aa(42) );

lcaa42:x= Run Program(//
		Executable( "PING.EXE" ), //
		Options( {"-n 50", "localhost"} ), //
		ReadFunction(
			Function( {this},
				write(this << read);
			)
		)
	);
	
wait(5); // report about 5 of the 50 pings to the log

// this will destroy the old object and replace it with a
// new one. The log will report the RunProgram object was
// destroyed; there may be a more clever way to witness the
// destruction...best I could come up with...
lcaa42 = New Object( aa(42.1) ); // the old one is gone
lcaa43 = New Object( aa(43) ); // the class still works
show(lcaa42:b,lcaa43:b); // 42.1,43
Show Classes();

Pinging v1-PC [::1] with 32 bytes of data:
Reply from ::1: time<1ms
Reply from ::1: time<1ms
Reply from ::1: time<1ms
Reply from ::1: time<1ms
Reply from ::1: time<1ms
Reply from ::1: time<1ms
The external program was producing output when the RunProgram object was destroyed.
Use a JSL variable to hold the RunProgram object.
Optionally, send messages to the variable to manage the object's lifetime.

lcaa42:b = 42.1;
lcaa43:b = 43;
// Class aa

_init_ = Method( {a}, this:b = a );
m1 = Method( {a, b}, a * b );
x = 1;

This shows the first object was deleted by assigning a new value to the variable holding it.

If other variables are copied (not cloned)

lcaa42b=lcaa42;

then all the copies must be cleared to destroy the object.

lcaa42b=0;
lcaa42=0;

@EvanMcCorkle

Re: Deleting Objects in v15

vince_faller — Tue, 19 Nov 2019 20:18:44 GMT

It seems like it's overwriting it if you just overwrite the variable. I ran

Names Default To Here( 1 );
Define Class(
	"Test",
	nObs = 20;
	addition = Method( {x, y},
		(x + y) * nObs
	);
	append = Method( {a, b},
		Char( a ) || " + " || Char( b )
	);
);

for(i=1, i<=1000000, i++, 
	clref = New Object( Test() );
);

delete symbols(clref);

While looking at the memory usage of JMP and it didn't really move. I would expect if it wasn't actually overwriting it I'd see memory go up if I have a million of them.

Re: Deleting Objects in v15

David_Burnham — Thu, 21 Nov 2019 10:14:05 GMT

Thanks everyone, I think the evidence if clear that reassigning an object variable destroys the object rather than leaving it as an orphan in memory,