Re: [boost] [asio] boost::asio::placeholders::error vs _1

From: Christopher Kohlhoff (chris_at_[hidden])
Date: 2006-02-26 07:51:33

Hi Jeff,

--- Jeff Flinn <TriumphSprint2000_at_[hidden]> wrote:

> What is the rationale for boost::asio::placeholders::error and 
> boost::asio::placeholders::bytes_transfered?

The named placeholders date from when some of the callback
handlers had arguments like "last_bytes_transferred" as well as
"total_bytes_transferred". Even though I wrote the functions, I
would forget the order of these parameters.

> I find this a foreign and confusing usage a boost::bind.
> Granted I jumped over the Tutorial explicitly introducing
> these, instead starting with the Tutorial DayTime.3 that
> addressed my interests. I see the familiar boost::bind, with
> the lack of _1, _2, so I'm thinking bind is generating a
> function of type void ()(). ... but handle_accept is expecting
> a boost::asio::error&???

That's why it's in a namespace called "placeholders" :) You
don't have to use the named placeholders if you don't want to,
but I find them a convenient aid in remembering and documenting
which arguments I'm expecting to go where.

Cheers,
Chris