Anton Davydov

Ruby tips #2

23 Nov 2016

It’s a second part of my post series about ruby tips. Today you’ll learn more about:

  • Special values
  • Symbol
  • Array
  • Hash
  • Range

CAUTION: These tips are not equally feat to production. Lots of them are just interesting solutions which you’ll not find anywhere else. Use them at your own risk.

Special values

Safe Levels

Full description

In ruby you can find security levels for your code. The Ruby security level is represented by the $SAFE global variable. The value ranges from minimum value 0 to maximum value 4.

$SAFE Constraints
0 No checking of the use of externally supplied (tainted) data is performed. This is Ruby’s default mode.
>= 1 Ruby disallows the use of tainted data by potentially dangerous operations.
>= 2 Ruby prohibits the loading of program files from globally writable locations.
>= 3 All newly created objects are considered tainted.
>= 4 Ruby effectively partitions the running program in two. Nontainted objects may not be modified. Typically, this will be used to create a sandbox: the program sets up an environment using a lower$SAFE level, then resets $SAFE to 4 to prevent subsequent changes to that environment.

Email Regexp

In ruby you can find regexp for emails. If you want to use it, you have to require uri library and call URI::MailTo::EMAIL_REGEXP constant.

DATA object

The global DATA variable in ruby allows us to access the text at the end of our file listed after the __END__ block. This can be surprisingly useful, for instance if we need to extract information from a rather large data blob.

# in one file
require "json"

puts JSON.load(DATA) # this DATA required text bellow __END__

__END__
{
  "records": [
    {
      "artist":"Iggy Pop",
      "title":"Lust for Life"
    },
    {
      "artist":"Television",
      "title":"Marquee Moon"
    },
    {
      "artist":"Talking Heads",
      "title":"Talking Heads: 77"
    }
  ]
}

Symbol

#all_symbols

Documentation

Return array with all symbols in env.

Symbol.all_symbols.size # => 5675

id2name

Documentation

Alias for #to_s (I don’t know why you need to use this but it’s a funny method I think).

:test.id2name   #=> "test"

slice

Documentation

Alias for sym.to_s[].

:hello_world.slice(0..4) #=> "hello"
:hello_world.[0..4]      #=> "hello"

Array

#bsearch

Documentation

ary = [0, 4, 7, 10, 12]
ary.bsearch {|x| x >=   4 } #=> 4
ary.bsearch {|x| x >=   6 } #=> 7
ary.bsearch {|x| x >=  -1 } #=> 0
ary.bsearch {|x| x >= 100 } #=> nil

Range to array

You can use * operator for converting range to array.

range = (1..10)

range.to_a == [*range] # => true

Hash

** method

You probably know already how to use * in method definition argument list. But ** is less known.

def method_name(value, *attr, **options)
  p attr
  p options
end

method_name('hello', 'cruel', 'world', collor: :red)
# => ['cruel', 'world']
# => { collor: :red }

Also you can call this method like [*attr]

hash = { a: :b, c: :d }

{ **hash, e: :f } # => {:a=>:b, :c=>:d, :e=>:f}

#gsub with hash args

str = "Help! All parentheses have been flipped )and I am sad(!"
str.gsub(/[\(\)]/, {"("=>")", ")"=>"("})
# => "Help! All parentheses have been flipped (and I am sad)!"

Non string and symbol keys

hash = { false => 'No', :to_s.to_proc => 'proc' }

hash[10 < 5]        # => "No"
hash[:to_s.to_proc] # => "proc"

Hash#assoc

This method returns a two element array [key, hash[key]]

{a: 1, b: 2}.assoc(:b) # => [:b, 2]

Range

#cover? and time

((Time.now - 1.hour)..(Time.now + 1.hour)).cover? (Time.now - 1.day) # => false
((Time.now - 1.hour)..(Time.now + 1.hour)).cover? Time.now           # => true

Ranges in case statements

age = 28

case age
when 01..17 then "Young"
when 18..50 then "Adult"
when 50..99 then "Old"
end

Conclusions

That’s all. I hope it’ll be useful for you. In next part we’re gonna talking about:

  • Tracing Ruby Code
  • memory usage
  • Enumerable
  • Compiler
  • Rspec
  • Rails

Happy hacking! 🚀

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