Re: [boost] New libraries implementing C++11 features in C++03

Subject: Re: [boost] New libraries implementing C++11 features in C++03
From: Brent Spillner (spillner_at_[hidden])
Date: 2011-11-25 15:45:20

On 25 Nov 2011 21:44:41 Dean Michael Berris wrote:
>function, it ceases to be a nameless function. The *utility* of having
>a function defined inside another function is marginal at best because
>they're absolutely better outside any other functions in all aspects:
>readability, maintainability, and functionality.

One of the many (often contradictory) heuristics for writing readable,
maintainable code is to put declarations near the site of use.  If you
have a function-like predicate that is only used in one or two places,
declaring it right before use makes it more likely that it will be
kept in sync with any changes to the calling code.  That can also make
it easier for someone else (including the future you) to read and
fully understand the code later, as less
backscrolling/cross-referencing/memorization is required to  fully
understand what's going on.  This is exactly the reason that literate
programming tools normally provide (and encourage) a mechanism to
interrupt the exposition of the calling function to define a callee,
and then return to the parent.  Like all other wisdom in this
discipline, it's not absolute, but local functions can be a more
useful organization tool than defining helper functions at namespace
scope.

>There's *no* practical reason to put a lambda in a named variable when
>the point of lambda's are so that you can define them in-line. I would

If they're stored in named variables, you can (more cleanly) switch
between two (or more) different predicates based on a runtime
condition.  You can also put them in an array or container and select
based on some key (e.g. for an event handler) or iterate over a subset
(e.g. repeating some for_each() loop with several different evaluation
metrics.)  Furthermore, giving something a name is an opportunity to
communicate something about your intent to a future reader--- if "_1 <
_2 ? _1 : _2" is named "select_max" then I can suspect a problem; if
it's anonymous I might not.  These are all the same reasons we put
function pointers and function objects in named variables and
containers--- sometimes it makes sense to organize the referent
functions at namespace scope, and sometimes it doesn't.