Re: [boost] Design conventions; passing functors

Subject: Re: [boost] Design conventions; passing functors
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2008-11-06 11:43:17

AMDG

Joachim Faulhaber wrote:
> <snip>
>
> template<class Domain, class Codomain, ...>
> class interval_map{
>   //(3) Adaptable functor
>   template<template<class>class Combinator>
>   interval_map& add(const value_type& value_pair,
>                     const Combinator<Codomain>& combine)
>   { /*combine functor passed or called somewhere*/  }
>   

Can't you use:

template<class Combinator>
interval_map& add(const value_type& value_pair, const Combinator& combine);
?

In other words, does Combinator really have to be a template?

> Now, there seems to be a convention from the STL that functors
> shall be passed BY VALUE.
>
> <snip>
>
> I do not really understand this convention and feel some
> resistance to follow it. In addition the call by value
> implementation can (and will) lead to heavy inefficiency
> by unaware usage of fat functors.

The assumption is that function objects are not fat.
If you have a large function object, it is always
possible to create another function object that just
stores a reference to the original function object.

>  So I browsed through
> some boost libraries and found that functors are passed by
> reference there (e.g. accumulators, fusion).
>
> Final question: What is the boost standard on passing functors,
> that I can adapt to?
>   

You can go either way.  There is no official Boost policy about this.

In Christ,
Steven Watanabe