Genadi Samokovarov

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Ruby Tips & Tricks #2: Lambda Literals in 1.9.3

Ruby 1.9.3 [support] is coming to an end and with it — an end of a syntax limitation. Welcome to the second Ruby Tips & Tricks post.

Have you ever wondered why the [community style guide] suggest you to write lambda literals like ->(a, b) { a + b } instead of -> (a, b) { a + b }? Well, there is a bit more than aesthetics to it…

In Ruby 1.9.3 -> (a, b) { a + b } isn’t syntactically valid:

>> -> (a, b) { a + b }
SyntaxError: (irb):1: syntax error, unexpected tLPAREN_ARG, expecting keyword_do_LAMBDA or tLAMBEG
-> (a, b) { a + b }
    ^
    from /1.9.3-p545/bin/irb:12:in `<main>'

The fore mentioned expression is valid in Ruby 2.0.0 and above. That’s what I call a significant whitespace!

Have you ever been bitten by it? Drop me a line on twitter at [@gsamokovarov].

[support]: https://www.ruby-lang.org/en/news/2014/01/10/ruby-1-9-3-will-end-on-2015/
[community style guide]...

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Ruby Tips & Tricks #1: Procs with Empty Blocks

Hello and welcome to the first Ruby Tips & Tricks post. In this series I would talk about interesting bits in Ruby.

Let’s start the series with a documented, but little known feature of the Proc.new constructor.

When Proc.new is called in a method with attached block, that block will be converted to a Proc object. Sounds confusing? An [example] shows it best:

def proc_from
  Proc.new
end

proc = proc_from { "hello" }
proc.call  => "hello"

When I first ran into code like this, it took me a while to digest it, even though this behaviour is [noted][example] pretty early in the [Proc] documentation.

Now that we know that it exists, how do we use it? Is it better than the more conventional example:

def proc_from(&block)
  block
end

proc = proc_from { "hello" }
proc.call  => "hello"

I believe it is! Why? In the conventional example, if there is no block given, block is nil. This...

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