From: Tobias Reif <tobiasreif@...>
Date: 2001-09-04T06:53:43+09:00
Subject: [ruby-talk:20817] Re: RCR: non-bang equivalent to []=

Matz,


> |I'd like to have bang and non-bang versions of each and every method.
> |The names should just differ in the !, like collect and collect!
> 
> Like scheme?  But imagine that every destructive (in other words, self
> modifying) method has ! in its name, Ruby programs would be filled
> with bangs.  It might be informative, but let's face it, it's ugly.


By reading the docs, everyone can find out how each method acts.
But a stringent concept would help programmers to always know how a 
method behaves in this aspect; which would benefit the Princple of Least 
Surprise.

If we were in the early phase (not having to consider finalized 
decisions, and backwards-compatibility):

If destructive methods are more often used that non-destructive one, the 
"default" (shorter name) could be destructive.
Otherwise, the default is to be non-destructive, like now.

I agree that '!'s all over the place could be ugly.
So maybe:
All methods are destructive by default, and every method has a 
counterpart which is non-destructive; since it returns a copy, _c could 
be appended (exact naming convention is just a detail of a stringent 
concept.).

Ruby is already at 1.7.x, so it's too late for all this.
Or is it?
Conventions for writing publicly available Ruby methods are interesting.
And Ruby 2 too.

Here are more thoughts:


I'm currently learning Ruby, and I like it a lot.

At first I thought that all methods return modified copies,
and only "!" methods modify the original.

Then I ran into many problems, because []=
is bang without having a "!" appended, and doesn't have
a non-bang version.

AFAIK, there are many more methods that are destructive but don't
declare that in their name:
clear, delete, delete_at, delete_if, fill, pop, push, replace, shift,
unshift, Array#filter.

It would be OK if all methods are bang by default, and have some
version which is non-bang.
But I think any stringent concept and naming convention not only
would immensely help beginners,
but add to Ruby's semantic richness and clarity.

Something like
"Beware, however, that there are a fair number of destructive methods
that don't have an '!' "
in the FAQs it not a nice discovery for everyone learning Ruby.
"The plain version takes a copy of the receiver, makes its change to it,
and returns the copy. The version with the ! modifies the receiver in 
place."
is a rule with many non-obvious exceptions.
This fact which generates confusion, and sabotages the
"Princple of Least Surprise" in a very relevant way.

Any concept would solve the problem, as long as it's 100% stringent.
(it could also be promoted as good style for all Ruby programs and libraries
that make methods available. For example:
Every method without a '!' makes a copy,
every method with a '!' is destructive.
Every method that is to be used by others
(in public classes, libraries, etc.) should consist of both versions.)

One possible concept:

(current, and stringent)
1. Variable assignment ist just that; nothing gets copied.
1.1. Use dup or clone to get a copy, and assign that.

(possible:)
2. Every method returns a (possibly modified) copy of what it
worked with.
2.2. Every method has a version that doesn't make a copy,
but directly works with the original.

Or:
(possible:)
2. Every method works directly with the original.
2.2. If you don't want to modify the original,
use dup or clone to get a copy and pass that.

Naming conventions like:
map, copy_and_map
or
map_original, map
or even
map_original, copy_and_map
are semantically rich, but too long.

So perhaps:

2. Every method returns a (possibly modified) copy of what it
worked with.
2.2. Every method has a version that doesn't make a copy,
but directly works with the original. The name of this
version is always the method name with an appended "!".

or:
2. Every method works directly with the original.
2.2. Every method has a version that makes a copy.
(Except where it's nonsenese:  #max, #first, #last (thanks David Black))
If you don't want to modify the original,
use dup or clone to get a copy and pass that;
or use the version of the method which returns a copy,
which declares that by having '_c' appended to it's name:
map_c

Tobi


-- 
Tobias Reif
http://www.pinkjuice.com/myDigitalProfile.xhtml

go_to('www.ruby-lang.org').get(ruby).play.create.have_fun
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