Re: [boost] [phoenix] default constructable stateless lambdas

Subject: Re: [boost] [phoenix] default constructable stateless lambdas
From: Mathias Gaunard (mathias.gaunard_at_[hidden])
Date: 2012-09-24 19:38:44

On 09/24/2012 09:01 PM, Eric Niebler wrote:
> While answering a question about Phoenix on stackoverflow[^1], I
> discovered that Phoenix lambda types are default-constructable, so long
> as all the terminals are also default constructable. That's handy when
> the terminals are stateless. Can it (the default-constructability) be
> relied on? It doesn't appear to be documented.

That's one of the advantages of taking holding children by value.
It also means Phoenix expressions could be serializable.

> C++11 lambdas have the nice property that stateless ones are implicitly
> convertible to raw function pointers. This can be implemented for
> Phoenix if we can rely on the default-constructability of Phoenix lambda
> types. In my stackoverflow answer I show how. It'd be pretty cool if
> this were a standard part of all Phoenix lambdas. Is there interest?

That probably requires that the function object be monomorphic too.