New features in ruby 2.3

ruby/new-features-in-ruby-2.3.md

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+# New features in ruby 2.3
+
+This update brings several new additions to core classes in ruby as well as some new syntax. Here are a few of the new additions coming in ruby 2.3:
+
+### 1. Extract values with Array#dig and Hash#dig
+
+The new #dig instance methods provide concise syntax for accessing deeply nested data. For example:
+
+```ruby
+user = {
+  user: {
+    address: {
+      street1: '123 Main street'
+    }
+  }
+}
+
+user.dig(:user, :address, :street1) # => '123 Main street'
+
+results = [[[1, 2, 3]]]
+
+results.dig(0, 0, 0) # => 1
+```
+
+Both of these methods will return nil if any access attempt in the deeply nested structure returns nil:
+```ruby
+user.dig(:user, :adddresss, :street1) # => nil
+user.dig(:user, :address, :street2) # => nil
+```
+
+### 2. Grep out the inverse of a pattern with Enumerable#grep_v
+
+This method is the inverse of the Enumerable#grep method. The grep method and its inverse provide several powerful ways to filter enumerables:
+Filtering by regular expression
+
+```ruby
+friends = %w[John Alain Jim Delmer]
+
+j_friends = friends.grep(/^J/)   # => ["John", "Jim"]
+others    = friends.grep_v(/^J/) # => ["Alain", "Delmer"]
+```
+
+Filtering by types
+```ruby
+items = [1, 1.0, '1', nil]
+
+nums   = items.grep(Numeric)   # => [1, 1.0]
+others = items.grep_v(Numeric) # => ['1', nil]
+```
+
+### 3. Fetching multiple values with Hash#fetch_values
+
+Sometimes Hash#fetch is a better choice than Hash#[] when you want to write more strict code. You can also access multiple values from a hash using Hash#values_at, but there wasn’t a strict equivalent to values_at until ruby 2.3:
+
+```ruby
+values = {
+  foo: 1,
+  bar: 2,
+  baz: 3,
+  qux: 4
+}
+
+values.values_at(:foo, :bar)    # => [1, 2]
+values.fetch_values(:foo, :bar) # => [1, 2]
+
+values.values_at(:foo, :bar, :invalid)    # => [1, 2, nil]
+values.fetch_values(:foo, :bar, :invalid) # => KeyError: key not found: :invalid
+```
+
+### 4. Positive and negative predicates for Numeric#positive? and Numeric#negative?
+Numeric values now have predicate methods that check if the subject is positive or negative. This can be useful if you want to filter an enumerable:
+```ruby
+numbers = (-5..5)
+
+numbers.select(&:positive?) # => [1, 2, 3, 4, 5]
+numbers.select(&:negative?) # => [-5, -4, -3, -2, -1]
+```
+
+### 5. Hash superset and subset operators Hash#<=, Hash#<, Hash#>=, and Hash#>
+These methods lets you compare hashes to see if they are subsets or proper subsets of each other. For example:
+```ruby
+small     = { a: 1                }
+medium    = { a: 1, b: 2          }
+large     = { a: 1, b: 2, c: 3    }
+different = { totally: :different }
+
+{ a: 1, b: 2 } > { a: 1 }             # => true
+{ a: 1 } > { a: 1 }                   # => false
+{ b: 1 } > { a: 1 }                   # => false
+{ a: 1, b: 2 } < { a: 1, b: 2, c: 3 } # => true
+```
+
+### 6. Convert a hash to a proc with Hash#to_proc
+Now you can use a hash to iterate over an enumerable object:
+```ruby
+hash = { a: 1, b: 2, c: 3 }
+keys = %i[a c d]
+
+keys.map(&hash) # => [1, 3, nil]
+```
+
+Avoid nil related errors with the safe navigation operator
+
+### 7. New syntax for accessing deeply nested objects safely without accidentally triggering a dreaded NoMethodError on nil. 
+The syntax looks like this:
+```ruby
+require 'ostruct'
+user&.address&.street&.first_line
+```
+
+where each instance of &. is similar to ActiveSupport’s Object#try method. Basically, if a nil value is encountered, then each method call will not be attempted and instead the nil value will be returned immediately.
+Experimental frozen string pragma
+
+You’ve probably heard that strings will be frozen by default in ruby 3. Ruby 2.3 lets you specify a pragma which enables this by default:
+```ruby
+$ ruby -v
+ruby 2.3.0preview1 (2015-11-11 trunk 52539) [x86_64-darwin14]
+$ cat default.rb
+# frozen_string_literal: false
+
+puts "Hello world".reverse!
+$ ruby default.rb
+dlrow olleH
+$ cat enabled.rb
+# frozen_string_literal: true
+
+puts "Hello world".reverse!
+$ ruby enabled.rb
+enabled.rb:3:in `reverse!': can't modify frozen String (RuntimeError)
+  from enabled.rb:3:in '<main>'
+```
+Alternatively, you can also enable and disable this using the command line argument --enable=frozen-string-literal