gmane.comp.finance.quantlib.devel

snovik | 21 Apr 17:17

Disposable<T>


Hi,

I am on the team to port ql to c# .net and trying to understand the reasons
behind Disposable<T> class. It looks to me like a tricky memory-saving
excercise and I wonder if it really is or there are other reasons.

would be very grateful.

rgds
s
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Luigi Ballabio | 29 Apr 17:55

Re: Disposable<T>

On Mon, 2008-04-21 at 08:19 -0700, snovik wrote:
> I am on the team to port ql to c# .net and trying to understand the reasons
> behind Disposable<T> class. It looks to me like a tricky memory-saving
> excercise and I wonder if it really is or there are other reasons.

It's not for saving memory---it's for performance. C++ has pass-by-copy
semantics. If we write:

Array operator*(Matrix, Array) {
    ...
    return a;
}

and then

u = M*v;

there will be at least one allocation and one copy of the array
elements, possibly two if the compiler doesn't optimize aggressively.
Disposable<T> removes some of them; not for saving memory, but for
saving time.  If C# returns values by reference, you don't need it in
your port.

Luigi

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Luigi Ballabio | 29 Apr 21:14

Re: Disposable<T>


On Apr 29, 2008, at 5:55 PM, Luigi Ballabio wrote:

> On Mon, 2008-04-21 at 08:19 -0700, snovik wrote:
>> I am on the team to port ql to c# .net and trying to understand the 
>> reasons
>> behind Disposable<T> class. It looks to me like a tricky memory-saving
>> excercise and I wonder if it really is or there are other reasons.
>
> It's not for saving memory---it's for performance. C++ has pass-by-copy
> semantics.

Also, the same applies to assignment. In C++, when we write

a = b;

you don't end up with two references (a and b) referring to the same 
instance. You end up with a being a new copy of b.

Luigi

P.S. I almost forgot---good luck with your C# port...

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