Re: [Boost-users] [boost-users][[proto] : Seeking advice on a DSL

Subject: Re: [Boost-users] [boost-users][[proto] : Seeking advice on a DSL
From: Manjunath Kudlur (keveman_at_[hidden])
Date: 2010-03-18 21:13:17

On Thu, Mar 18, 2010 at 4:23 PM, Eric Niebler <eric_at_[hidden]> wrote:
> That is an interesting approach. The two problems I see are:
>
> 1) Your use of BOOST_AUTO leaves a bunch of dangling references and creates
> undefined behavior. As you have it defined, program_generator no longer has
> the effect of deep-copying the expression tree. Try displaying
> typeid(p).name() and see, for instance, that the intermediate expressions
> are stored by reference, and the literal 2 is stored by int const&. Any
> attempt to use p will likely expode sooner or later. The fix is to deep-copy
> the expression when you wrap it in program_expr, but a simple deep-copy will
> break your scheme because every program_variable will be deep-copied too. A
> simple fix would be to make program_variable<T> a wrapper for a
> boost::shared_ptr<T>, but ...
>
> 2) Your program objects are not thread safe. Since they contain mutable
> data, you can't stick the program in, say, a boost::function, make a few
> copies and evaluate them concurrently within different threads. That may not
> be important to you, but I consider it a pretty serious shortcoming.

I did think about thread-safety. The in-place approach is definitely
not thread-safe. But under restricted conditions (single-threaded,
evaluated in the same scope as the free variables), and a reasonable
optimizing compiler, the performance of this method should approach
hand-coded C, no?

Manjunath