what is the interest of In Place factory

[rodrigue pons]

Hello,

I was looking about the boost In Place Factory to resolve a problem i
got, and there is something i don't understand: what is the advantage
of this lib?


For example:

I get a class A, wich constructor is:
A( int, const string& );

And an another class, C, that contains an A*. C provides a method to
construct this A*:
void C::BuildA( int i, const string & str );

wich will be called this way:
instance_of_C.BuildA( 1, "test" );


If now i use the boost In Place Factory, the member function C::BuildA
will become:

template<class InPlaceFactoryT>
void C::BuildA( InPlaceFactoryT const& factory )

wich will be called this way:
instance_of_C.BuildA( 1, "test" );


We can see here that with or wothout the In Place Factory, the code is
exactly the same. So i guess there is something i didn't understand.
But what?
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[Stefan Strasser-2]

Am Thursday 29 October 2009 15:35:52 schrieb rodrigue pons:

> Hello,
>
> I was looking about the boost In Place Factory to resolve a problem i
> got, and there is something i don't understand: what is the advantage
> of this lib?
>
>
> For example:
>
> I get a class A, wich constructor is:
> A( int, const string& );
>
> And an another class, C, that contains an A*. C provides a method to
> construct this A*:
> void C::BuildA( int i, const string & str );
>
> wich will be called this way:
> instance_of_C.BuildA( 1, "test" );
>
>
> If now i use the boost In Place Factory, the member function C::BuildA
> will become:
>
> template<class InPlaceFactoryT>
> void C::BuildA( InPlaceFactoryT const& factory )
>
> wich will be called this way:
> instance_of_C.BuildA( 1, "test" );
>
>
> We can see here that with or wothout the In Place Factory, the code is
> exactly the same. So i guess there is something i didn't understand.
> But what?

the type of A might be unknown to the author of C, i.e. dependent on a
template parameter. so C cannot know the number and types of parameters to
the constructor of A.
see boost::optional<> for a use case.
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[rodrigue pons]

Haaa okay i see.
Thank you :)

2009/10/29 Stefan Strasser <strasser@...>:

> Am Thursday 29 October 2009 15:35:52 schrieb rodrigue pons:
>> Hello,
>>
>> I was looking about the boost In Place Factory to resolve a problem i
>> got, and there is something i don't understand: what is the advantage
>> of this lib?
>>
>>
>> For example:
>>
>> I get a class A, wich constructor is:
>> A( int, const string& );
>>
>> And an another class, C, that contains an A*. C provides a method to
>> construct this A*:
>> void C::BuildA( int i, const string & str );
>>
>> wich will be called this way:
>> instance_of_C.BuildA( 1, "test" );
>>
>>
>> If now i use the boost In Place Factory, the member function C::BuildA
>> will become:
>>
>> template<class InPlaceFactoryT>
>> void C::BuildA( InPlaceFactoryT const& factory )
>>
>> wich will be called this way:
>> instance_of_C.BuildA( 1, "test" );
>>
>>
>> We can see here that with or wothout the In Place Factory, the code is
>> exactly the same. So i guess there is something i didn't understand.
>> But what?
>
> the type of A might be unknown to the author of C, i.e. dependent on a
> template parameter. so C cannot know the number and types of parameters to
> the constructor of A.
> see boost::optional<> for a use case.
> _______________________________________________
> Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
>

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