[parameter] Parameter-Enabled Class Templates: combining keyword and deduction for the same parameter

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Joaquín Mª López Muñoz

19 Jul 2007 19 Jul '07

3:51 p.m.

The docs explain that a parameter can be named: typedef parameter::parameters< requiredtag::threading_policy ...

...

class_signature; ... class_,...>;

or else be deduced: typedef parameter::parameters< required< deducedtag::threading_policy, is_base_and_derived > ...

...

class_signature; ... class multithreaded: threading_policy_marker{...}; class_;

Now, is it possible to combine these two options into one, so that the the two syntaxes class_,...>; class_; are accepted? If so, how? Thank you, Joaquín M López Muñoz Telefónica, Investigación y Desarrollo

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David Abrahams

19 Jul 19 Jul

7:02 p.m.

New subject: [parameter] Parameter-Enabled Class Templates: combining keyword and deduction for the same parameter

on Thu Jul 19 2007, Joaquín Mª López Muñoz wrote:

...

The docs explain that a parameter can be named:

typedef parameter::parameters< requiredtag::threading_policy ...

...
class_signature; ... class_,...>;

or else be deduced:

typedef parameter::parameters< required< deducedtag::threading_policy, is_base_and_derived > ...

...
class_signature; ... class multithreaded: threading_policy_marker{...}; class_;

Now, is it possible to combine these two options into one, so that the the two syntaxes

class_,...>; class_;

are accepted? If so, how?

Just used deducedtag::threading_policy; deduced parameters can be deduced from argument types or from the names attached to named arguments. -- Dave Abrahams Boost Consulting http://www.boost-consulting.com The Astoria Seminar ==> http://www.astoriaseminar.com

"JOAQUIN LOPEZ MU?Z"

7:18 p.m.

New subject: [parameter] Parameter-Enabled Class Templates:combining keyword and deduction for the same parameter

----- Mensaje original ----- De: David Abrahams Fecha: Jueves, Julio 19, 2007 9:06 pm Asunto: Re: [Boost-users] [parameter] Parameter-Enabled Class Templates:combining keyword and deduction for the same parameter Para: boost-users@lists.boost.org

...

on Thu Jul 19 2007, Joaquín Mª López Muñoz wrote:

...
The docs explain that a parameter can be named:

typedef parameter::parameters< requiredtag::threading_policy ...

...
class_signature; ... class_,...>;

or else be deduced:

typedef parameter::parameters< required< deducedtag::threading_policy, is_base_and_derived > ...

...
class_signature; ... class multithreaded: threading_policy_marker{...}; class_;

Now, is it possible to combine these two options into one, so that the two syntaxes

class_,...>; class_;

are accepted? If so, how?

Just used deducedtag::threading_policy; deduced parameters can be deduced from argument types or from the names attached to named arguments.

Just to be sure: so, given the parameter specification requiredtag::T,F>, Boost.Parameter matches it to T<X> even if X does *not* satisfy F, correct? Thank you, Joaquín M López Muñoz Telefónica, Investigación y Desarrollo

David Abrahams

9:19 p.m.

New subject: [parameter] Parameter-Enabled Class Templates:combining keyword and deduction for the same parameter

on Thu Jul 19 2007, "JOAQUIN LOPEZ MU?Z" wrote:

...

Just to be sure: so, given the parameter specification

requiredtag::T,F>,

Boost.Parameter matches it to T<X> even if X does *not* satisfy F, correct?

That's the intention... although I can't promise SFINAE won't kick in in some cases. -- Dave Abrahams Boost Consulting http://www.boost-consulting.com The Astoria Seminar ==> http://www.astoriaseminar.com

Daniel Wallin

9:58 p.m.

New subject: [parameter] Parameter-Enabled Class Templates:combining keyword and deduction for the same parameter

David Abrahams wrote:

...

on Thu Jul 19 2007, "JOAQUIN LOPEZ MU?Z" wrote:

...
Just to be sure: so, given the parameter specification

requiredtag::T,F>,

Boost.Parameter matches it to T<X> even if X does *not* satisfy F, correct?

That's the intention... although I can't promise SFINAE won't kick in in some cases.

Joaquin was talking about class templates, so the above holds true. SFINAE will kick in if you use the restriction mechanism for function templates. The PP interface does that, so if you use that you can't supply parameter types that doesn't match the predicate. -- Daniel Wallin Boost Consulting www.boost-consulting.com

"JOAQUIN LOPEZ MU?Z"

10:55 p.m.

New subject: [parameter] Parameter-Enabled Class Templates:combining keyword and deduction for the same parameter

----- Mensaje original ----- De: Daniel Wallin Fecha: Viernes, Julio 20, 2007 0:11 am Asunto: Re: [Boost-users] [parameter] Parameter-Enabled Class Templates:combining keyword and deduction for the same parameter Para: boost-users@lists.boost.org

...

David Abrahams wrote:

...
on Thu Jul 19 2007, "JOAQUIN LOPEZ MU?Z" wrote:

...
Just to be sure: so, given the parameter specification

requiredtag::T,F>,

Boost.Parameter matches it to T<X> even if X does *not* satisfy F, correct?

That's the intention... although I can't promise SFINAE won't kick in in some cases.

Joaquin was talking about class templates, so the above holds true. SFINAE will kick in if you use the restriction mechanism for function templates. The PP interface does that, so if you use that you can't supply parameter types that doesn't match the predicate.

I've read this over and over and can't say whether you're correcting Dave or me :( excuse my incompetence. So, given (in the context of class template parameters) requiredtag::T,F>, can Boost.Parameter match it to T<X> even if X does *not* satisfy F? Thank you! Joaquín M López Muñoz Telefónica, Investigación y Desarrollo

Daniel Wallin

27 Jul 27 Jul

8:10 p.m.

New subject: [parameter] Parameter-Enabled Class Templates:combining keyword and deduction for the same parameter

JOAQUIN LOPEZ MU?Z wrote:

...

----- Mensaje original ----- De: Daniel Wallin Fecha: Viernes, Julio 20, 2007 0:11 am Asunto: Re: [Boost-users] [parameter] Parameter-Enabled Class Templates:combining keyword and deduction for the same parameter Para: boost-users@lists.boost.org

...
David Abrahams wrote:

...
on Thu Jul 19 2007, "JOAQUIN LOPEZ MU?Z" wrote:

...
Just to be sure: so, given the parameter specification

requiredtag::T,F>,

Boost.Parameter matches it to T<X> even if X does *not* satisfy F, correct? That's the intention... although I can't promise SFINAE won't kick in in some cases. Joaquin was talking about class templates, so the above holds true. SFINAE will kick in if you use the restriction mechanism for function templates. The PP interface does that, so if you use that you can't supply parameter types that doesn't match the predicate.

I've read this over and over and can't say whether you're correcting Dave or me :( excuse my incompetence. So, given (in the context of class template parameters)

requiredtag::T,F>,

can Boost.Parameter match it to T<X> even if X does *not* satisfy F? Thank you!

Yes, that is correct. However, is you use `parameters::match<>` to restrict a function template, SFINAE will kick in. For example: BOOST_PARAMETER_FUNCTION((void), f, tag, (deduced (required (x, (std::string))) ) ); f(x = 10); // no overload matches -- Daniel Wallin Boost Consulting www.boost-consulting.com

Joaquin M Lopez Munoz

28 Jul 28 Jul

8 a.m.

New subject: [parameter] Parameter-Enabled Class Templates:combining keyword and deduction for the same parameter

Daniel Wallin writes:

...

JOAQUIN LOPEZ MU?Z wrote:

[...]

...

...
I've read this over and over and can't say whether you're correcting Dave or me :( excuse my incompetence. So, given (in the context of class template parameters)

requiredtag::T,F>,

can Boost.Parameter match it to T<X> even if X does *not* satisfy F? Thank you!

Yes, that is correct. However, is you use `parameters::match<>` to restrict a function template, SFINAE will kick in. For example:

BOOST_PARAMETER_FUNCTION((void), f, tag, (deduced (required (x, (std::string))) ) );

f(x = 10); // no overload matches

OK, thanks for the info! Since it's only class templates that I'm interested, the behavior is exactly what I need. In the meantine, I've tried the lib and learnt the additional fact that, for requiredtag::T,F>, if T<X> is passed and T<X> (rather than X) satisfies F, then Boost.Parameter returns X as the matched arg rather than T<X>. Not that this poses any particular difficulty with what I'm trying to use the lib for, but it's a somewhat corner case I'd like to share with you. BTW, Boost.Parameter is a pleasure to work with! I hope to be able to show soon a B.P-powered lib where your stuff makes it a joy, both for the lib writer and the user, to deal with class templates with lots of parameters. Best, Joaquín M López Muñoz Telefónica, Investigación y Desarrollo

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"JOAQUIN LOPEZ MU?Z"
Daniel Wallin
David Abrahams
Joaquin M Lopez Munoz
Joaquín Mª López Muñoz