On Thu, Jul 17, 2008 at 4:50 PM, Andrey Semashev <andrey.semashev@gmail.com> wrote:

Robert Jones wrote:

...

Given a bit of code like this,

struct S { bool pred( ) const; };

typdef vector<pair<string, S *> > V; V :: const_iterator i;

i -> second -> pred( );

I'd like to rewrite the last line as a lambda expression. Looking at the documentation, I think this is done with

bind( & S :: pred, bind( & V :: value_type :: second, _1 ) )( * i );

which works. But I'd rather be writing something like

( _1 -> second -> pred )( * i );

Am I right in thinking that Boost.Lambda just doesn't work like this, and the frst form is how it's done?

It doesn't work because Lambda's operator-> won't be able to provide second or pred in its result.

You can do this, however:

typedef V::value_type VT;

bind(&S::pred, &_1->*&VT::second)

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Ah... that 's getting there! And so presumably by extension I can write & ( & _1 ->* & V :: value_type :: second ) ->* & S :: pred; or is that a step too far? -- ACCU - Professionalism in programming - http://www.accu.org

On Thu, Jul 17, 2008 at 9:11 PM, Steven Watanabe <watanabesj@gmail.com> wrote:

AMDG

Robert Jones wrote:

...

Ah... that 's getting there! And so presumably by extension I can write

& ( & _1 ->* & V :: value_type :: second ) ->* & S :: pred;

or is that a step too far?

I think that you would actually need (untested):

bind(&( & _1 ->* & V :: value_type :: second ) ->* & S :: pred)

It's minefield! I too am away from a compiler - I'll give a few options a whirl when I'm back in the office. Thanks, Rob.