[Fusion] Adapting read-only fields of ADTs
Hi, How would I use BOOST_FUSION_ADAPT_ADT to turn an ADT that doesn't expose setters into a read-only sequence? In other words, what do I pass as set_exprN if there is no valid set expression? Sebastian
On Mon, Apr 11, 2011 at 9:18 AM, Sebastian Redl <sebastian.redl@getdesigned.at> wrote:
Hi,
How would I use BOOST_FUSION_ADAPT_ADT to turn an ADT that doesn't expose setters into a read-only sequence? In other words, what do I pass as set_exprN if there is no valid set expression?
Just pass it nothing. e.g. BOOST_FUSION_ADAPT_ADT( name, (std::string const&, std::string const&, obj.get(), ) ; -- Eld på åren og sol på eng gjer mannen fegen og fjåg. [Jøtul] <demo> 2011 Tore Halvorsen || +052 0553034554
On 4/11/2011 7:05 PM, Tore Halvorsen wrote:
On Mon, Apr 11, 2011 at 9:18 AM, Sebastian Redl <sebastian.redl@getdesigned.at> wrote:
Hi,
How would I use BOOST_FUSION_ADAPT_ADT to turn an ADT that doesn't expose setters into a read-only sequence? In other words, what do I pass as set_exprN if there is no valid set expression?
Just pass it nothing.
e.g.
BOOST_FUSION_ADAPT_ADT( name, (std::string const&, std::string const&, obj.get(), ) ;
That's a good workaround, but really, we ought to have read-only adaptors. Doing above would still allow elem = val; albeit will be a no-op. Please add a trac "feature request" ticket, if you will. Regards, -- Joel de Guzman http://www.boostpro.com http://boost-spirit.com
Joel de Guzman <joel@boost-consulting.com> writes: [...]
That's a good workaround, but really, we ought to have read-only adaptors. Doing above would still allow elem = val; albeit will be a no-op.
Please add a trac "feature request" ticket, if you will.
Regards,
A simple workaround is to fall back to an invalid expression. --8<---------------cut here---------------start------------->8--- #include<boost/fusion/adapted.hpp> #include<boost/fusion/sequence.hpp> template<typename>struct dummy{}; template<typename T> typename dummy<T>::this_type_does_not_exist invalid_operation(T const&) {} class A{}; BOOST_FUSION_ADAPT_ADT(A,(int,int,1,invalid_operation(val))) int main() { A a; boost::fusion::front(a)=1; } --8<---------------cut here---------------end--------------->8--- This should give a nice and readable error message. -Christopher
On 4/13/2011 1:18 AM, Christopher Schmidt wrote:
Joel de Guzman<joel@boost-consulting.com> writes:
[...]
That's a good workaround, but really, we ought to have read-only adaptors. Doing above would still allow elem = val; albeit will be a no-op.
Please add a trac "feature request" ticket, if you will.
Regards,
A simple workaround is to fall back to an invalid expression.
[...] Good idea, Christopher! So perhaps this is just a matter of documentation? Regards, -- Joel de Guzman http://www.boostpro.com http://boost-spirit.com
participants (4)
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Christopher Schmidt -
Joel de Guzman -
Sebastian Redl -
Tore Halvorsen