Re: [boost] Proposal: converting casts for 'any'

From: Corwin Joy (cjoy_at_[hidden])
Date: 2001-07-19 02:39:49

One other point.  One also gets semi-scripting capabilities from any_ccast
e.g.

any a(double(2.5)), b(int(3));

any c= any_ccast<double>(a) + any_ccast<double>(b);

assigns c a type of double with a value of 5.5

CJ

----- Original Message -----
From: "Corwin Joy" <cjoy_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Thursday, July 19, 2001 2:10 AM
Subject: [boost] Proposal: converting casts for 'any'

> I have uploaded to the boost website a set of files for registering and
> performing conversion casts with an 'any' object into the folder
any_ccast.
> This can be done without making modifications to the current 'any'
> structure. The syntax for this cast looks like this:
>
> any_ccast ('any' converting cast)
>
> template<typename ValueType>
>   ValueType any_ccast(const any & operand);
>
> Custom keyword cast for extracting a value of a given type from an any
with
> a possible conversion to get the requested type. If the conversion from
the
> type held by any to the requested value type is allowed then this returns
a
> copy of the extracted result if successful, otherwise a bad_cast exception
> is thrown. any_ccast is normally used when you don't know the exact type
> held by an 'any' variable and you want to request a (possibly) converting
> cast to a given format.
>
>
> Examples:
>
> any a(double(3.5));
>
> // These will invoke boost::numeric_cast
> cout << any_ccast<int>(a) << endl;  // cast out 'any' contents to an int
> cout << any_ccast<float>(a) << endl; // cast out 'any' contents to a float
>
> // This will use boost::lexical_cast
> cout << any_ccast<string>(a) << endl; // cast out 'any' contents to string
>
> similarly, one can write:
>
> any a(string("12345"));
> cout << any_ccast<int>(a) << endl;  // lexical cast to an int
>
> etc.
>
> For more examples see the documentation and tests in the uploaded folder.
>
> Users can also add their own classes and user defined casts as shown in
the
> cast_registry constructor in any_ccast.cpp.  Essentially the syntax is
just:
>
> g_cast_registry.add_cast_fn(id_for_target_type, id_for_source_type,
>   pointer_to_cast_function);
>
> see any_ccast.cpp for details.
>
>
>
>
>
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