Re: [boost] [Proto] Copying expressions

From: Maurizio Vitale (maurizio.vitale_at_[hidden])
Date: 2007-07-17 08:48:04

bitten by this in the past. There's a proto::deep_copy function that  
you can use for converting references to values.
Regards,
                Maurizio

On Jul 17, 2007, at 2:54 AM, dan marsden wrote:

> Hi
>
> I'm creating lambda expressions using proto, using the extension  
> mechanism to add my own operator() so that I can do:
>
> (_0 += _1)(x,y)
>
> The operator() does all the transforming of the expression tree,  
> and evaluates the result. The above works ok, its pretty similar to  
> your calculator examples.
>
> If I want to do something like
>
> function<int(int&,int&)> f(_0 + _1); // Copy lambda expression into  
> a Boost.Function func
>
> Now I've got problems because proto trees are built out of  
> references (to temporaries). So func will blow up later when the  
> temporaries are off the stack (actually the example I've tried  
> starts evaluating junk values). I believe the above code will work  
> today with BLL and Phoenix, as the temporaries are copied rather  
> than handled as references.
>
> As I cannot interfere with the Boost.Function constructors, how can  
> I transform my expression tree to change the refs to copies, whilst  
> retaining the syntax above? Is there some way to tell proto to  
> build trees with copies? Or have I missed something clever in proto  
> again :) It might make a good Calc4 example as I imagine this is a  
> common requirement.
>
> Cheers
>
> Dan
>
>
>
>
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