ifelse¶ ↑

github.com/jimwise/ifelse

Author

Jim Wise (jwise@draga.com)

Copyright

Copyright © 2013 Jim Wise

License

2-clause BSD-Style (see LICENSE.txt)

IfElse is an implementation of the pure object-oriented conditional syntax found in languages of the SmallTalk family, including Self. Those languages distinguish themselves by taking the “everything is an object / everything is a method” approach to a further extreme than Ruby, and getting rid of almost all cases of special syntax other than object definition and method call.

Ruby, of course, already works this way for some purposes – thus most Ruby developers prefer to write

[1, 17, 39].each {|x| puts x}

rather than

for x in [1, 17, 39]
  puts x
end

and

3.times {|n| puts n}

instead of

i = 1
while i <= 3
  puts i
  i += 1
end

This module extends that same preference to conditional statements, providing replacements for the Ruby keywords if, and unless:

x = 1
(x >= 0).if {puts 'positive'}
(x < 0).unless {puts 'positive'}

Note that as with the built-in special forms these methods replace, these methods are available on any Ruby Object, and obey the usual rules of which values are considered “Truthy” and “Falsey”.

Note that the primary purpose of this gem is to demonstrate that the built-in (special form) versions of conditionals provided with Ruby are mostly syntactic sugar – as with the for keyword, there is no real need for these to be built into the language. With that said, the gem is fully tested, has no particular performance penalty (beyond the usual cost of method dispatch), and should be fully useable in general purpose code.

Note also that while Smalltalk-family languages also provide an equivalent to the Ruby else keyword, this depends on the more general block/lambda capability of those languages, which allow a method to take multiple blocks as arguments. This could be imitated with a syntax like:

# NOT A REAL EXAMPLE
(x > 42).if then: lambda {|x| :big }, else: lambda {|x| :small}

which is true to the SmallTalk original, but feels less Ruby-ish to me, so I didn’t implement this – perhaps in a later version.

IfElse has been tested on Ruby 1.9.3 and above (including 2.0.0), though it should work fine on earlier versions (drop me an email if you try it out there). IfElse has no other dependencies.

This class provides two methods, implemented on every ruby Object (but see NOTES, below):

#if

This method takes a block, which will be executed only if the object it is called on has a “Truthy” value (neither false nor nil – but see below). The block may take one argument, which will be passed the value which was tested, if present. The return value of this method is the value of the block, if it is invoked, or the original (Falsey) value the method was called on otherwise. For example:

h[:foo].if {|x| puts x}       # outputs the value of h[:foo], if present

#unless

This method takes a block, which will be executed only if the object it is called on has a “Falsey” value (either false or nil – but see below). The block may take one argument, which will be passed the value which was tested, if present. The return value of this method is the value of the block, if it is invoked, or the original (Truthy) value the method was called on otherwise. For example:

h[:bar].unless {|x| puts 'missing'} # outputs 'missing' if key :bar
                        # is not present in h

As a demonstration of the added flexibility provided by replacing special syntax with an object-oriented approach, this gem provides one additional feature: when defining a class, you may decide for yourself whether values of that class should be considered “Truthy” or “Falsey”.

This is done by including the Modules IfElse::TrueIfBehavior or IfElse::FalseIfBehavior in your class (of course, values other than ‘false’ and ‘nil’ are true by default, so you will normally only need to use the latter. For example, after:

class List
   ...
end

class Empty List < List
  include IfElse::FalseIfBehavior

  ...
end

Values of class EmptyList are now Falsey for the purposes of #if and #unless, while values of type List remain Truthy.

*

That is, any subclass of Object – these forms are not available on classes which only subclass BasicObject, to ease implementation.

$ gem install ifelse

After checking out the source, run:

$ rake newb

This task will install any missing dependencies, run the tests/specs, and generate the RDoc.

(The MIT License)

Copyright © 2013 FIX

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the ‘Software’), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED ‘AS IS’, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.