[boost] [phoenix] default constructable stateless lambdas

Subject: [boost] [phoenix] default constructable stateless lambdas
From: Eric Niebler (eric_at_[hidden])
Date: 2012-09-24 15:01:55

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.

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?

Incidentally, I think it's really, really cool that Phoenix allows this
kind of extensibility. It's a very nice example of the benefits of the
introspection capabilities built into Phoenix. Perhaps this could be
worked into the docs somehow?

[^1]:
http://stackoverflow.com/questions/10144948/static-functions-from-boost-lambda-or-boost-phoenix/12326204#12326204

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com