Returning an array of double's: which COM/OLE type is better?

[Giovanni Dicanio]

Suppose we are developing a COM server exposing an interface with a method
to return an array of double's to the caller.

I think that there are four options to define this output parameter (which
is an array of double's):

1. SAFEARRAY of double's
2. SAFEARRAY of VARIANT's (each VARIANT being a double)
3. VARIANT which is a SAFEARRAY of double's
4. VARIANT which is a SAFEARRAY of VARIANT's (each VARIANT being a double)

Is there any rule or guideline to follow to choose the right option?
Is there any particular advantage in choosing one respect to others?

Thanks,
Giovanni

[Igor Tandetnik]

Giovanni Dicanio wrote:
> Suppose we are developing a COM server exposing an interface with a
> method to return an array of double's to the caller.
>
> I think that there are four options to define this output parameter
> (which is an array of double's):
>
> 1. SAFEARRAY of double's
> 2. SAFEARRAY of VARIANT's (each VARIANT being a double)
> 3. VARIANT which is a SAFEARRAY of double's
> 4. VARIANT which is a SAFEARRAY of VARIANT's (each VARIANT being a
> double)
>
> Is there any rule or guideline to follow to choose the right option?

KISS (http://simple.wikipedia.org/wiki/K.I.S.S.)

Most of the time, I'd go with #1, as expressing my intent most directly. However, if your component has to be used from VBScript, then go with #2 - VBScript can only handle a safearray of variants.
--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not necessarily a good idea. It is hard to be sure where they are going to land, and it could be dangerous sitting under them as they fly overhead. -- RFC 1925

[Giovanni Dicanio]

"Igor Tandetnik" <itand...@mvps.org> ha scritto nel messaggio
news:u6fOkSzS...@TK2MSFTNGP04.phx.gbl...

> KISS (http://simple.wikipedia.org/wiki/K.I.S.S.)
>
> Most of the time, I'd go with #1, as expressing my intent most directly.
> However, if your component has to be used from VBScript, then go with #2 -
> VBScript can only handle a safearray of variants.

Thank you,
Giovanni

[Brian Muth]

Giovanni, I concur with Igor. If you want it scriptable, then use either 2
or 4 (my own preference is 4). Otherwise, I'd use 1.

Brian

[Giovanni Dicanio]

"Brian Muth" <bm...@mvps.org> ha scritto nel messaggio
news:45698A77-F3B4-494C...@microsoft.com...

> Giovanni, I concur with Igor. If you want it scriptable, then use either 2
> or 4 (my own preference is 4). Otherwise, I'd use 1.

Thanks Brian.

In case of scriptable component, why do you prefer 4 instead of 2?

Is the intent more clear when using a SAFEARRAY (2) instead of a VARIANT
which is a SAFEARRAY (4) ?
Or, in case of scriptable component, would you just use VARIANT's everywhere
(e.g. also for scalar integer type, etc.)?

Using VARIANT's seems to me like giving a more "dynamic" look to the
component interface, but IMHO I would prefer making the intent more clear,
so using VARIANT's as few as possible.

Thanks,
Giovanni

[Jim Barry]

Giovanni Dicanio wrote:
> Is the intent more clear when using a SAFEARRAY (2) instead of a VARIANT
> which is a SAFEARRAY (4) ?
> Or, in case of scriptable component, would you just use VARIANT's
> everywhere (e.g. also for scalar integer type, etc.)?

Scripting languages access COM objects through IDispatch, so each
non-VARIANT parameter or return value is automatically wrapped in a
VARIANT. It only makes any difference to clients that access custom
interfaces (or dual interfaces via vtable methods).

- Jim

[Giovanni Dicanio]

"Jim Barry" <j...@mvps.org> ha scritto nel messaggio
news:#5fLrhPT...@TK2MSFTNGP05.phx.gbl...

> Scripting languages access COM objects through IDispatch, so each
> non-VARIANT parameter or return value is automatically wrapped in a
> VARIANT. It only makes any difference to clients that access custom
> interfaces (or dual interfaces via vtable methods).

Thanks Jim!

Giovanni