Re: [boost] [proto] transform for flattening an expression - how?

From: Eric Niebler (eric_at_[hidden])
Date: 2008-03-20 17:50:06

Markus Werle wrote:
> Actually I thought that transforms only work on expr<> 
> not on fusion sequences. I just don't want to switch the
> library in order to do all this CT magic.

Right, transforms accept expressions. There's nothing stopping you from 
writing a transform that accepts an expression, creates a flat view, and 
manipulates the flat view with Fusion algorithms. In fact, there is a 
Proto transform that does just that: fold<>. When you use 
transform::fold<Seq, State, Fun>, Seq is a transform that accepts an 
expression and returns a Fusion sequence. The fold<> transform then just 
calls fusion::fold() on that sequence.

Usually Seq is proto::_, which causes you to fold the children of the 
current expression. That's because "_" is an identity transform ... it 
just returns the expression passed to it. And expressions are valid 
Fusion sequences of their children.

My point is, you don't have to "switch libraries" ... you can use them 
both because they're designed to work together.

-- 
Eric Niebler
Boost Consulting
www.boost-consulting.com