Difference Between "And" and && in Ruby

Difference between .. and ... in Ruby

In ruby 1...5 gives you a range which doesn't include 5
whereas 1..5 gives you a range which does include 5

eg:

>> (1..5).to_a
[
    [0] 1,
    [1] 2,
    [2] 3,
    [3] 4,
    [4] 5
]
>> (1...5).to_a
[
    [0] 1,
    [1] 2,
    [2] 3,
    [3] 4
]

Difference between and and && in Ruby?

and is the same as && but with lower precedence. They both use short-circuit evaluation.

WARNING: and even has lower precedence than = so you'll usually want to avoid and. An example when and should be used can be found in the Rails Guide under "Avoiding Double Render Errors".

What is the difference between += and =+ in Ruby?

1. a += b is syntactic shorthand for a = a + b
2. a =+ b is similar to a = + b

So, firstValue = firstValue + secondValue is the same as firstValue = firstValue.+(secondValue) in ruby.
firstValue + = secondValue – increment Add the value of secondValue to the value of firstValue , store the result in firstValue, and return the new value.

what is the difference between += and =+ in ruby?

There's no such token as =+; it's actually two tokens: assignment followed by the unary + operator; the latter is essentially a no-op, so @@num_things =+ 1 is equivalent to @@num_things = 1.

Since there is a += token, the language parser will parse it as a single token.

(In the early formulations of BCPL which was the precursor to C, the modern -= operator was written as =-.)

What is the difference between @@ and @ in Ruby?

A variable prefixed with @@ is a class variable and one prefixed with @ is an instance variable. A great description can be found in this answer: https://stackoverflow.com/a/5890199/1181886

Difference between or and || in Ruby?

It's a matter of operator precedence.

|| has a higher precedence than or.

So, in between the two you have other operators including ternary (? :) and assignment (=) so which one you choose can affect the outcome of statements.

Here's a ruby operator precedence table.

See this question for another example using and/&&.

Also, be aware of some nasty things that could happen:

a = false || true  #=> true
a  #=> true

a = false or true  #=> true
a  #=> false

Both of the previous two statements evaluate to true, but the second sets a to false since = precedence is lower than || but higher than or.

What's the difference between or and | in ruby?

The | operator is a binary mathematical operator, that is it does a binary OR and works on a numerical level:

1 | 2
# => 3
4 | 3
# => 7
1 | 2 | 3
# => 3

This is because it's manipulating individual values as if they were binary:

0b01 | 0b10
# => 3 (0b11)

The || operator is a logical one, that is it returns the first value that's logically true. In Ruby only literal nil and false values evaluates as logically false, everything else, including 0, empty strings and arrays, is true.

So:

1 || 2
# => 1
0 || 1
# => 0

The or operator works almost exactly the same as || except it's at a much lower precedence. That means other operators are evaluated first which can lead to some problems if you're not anticipating this:

a = false || true
# => true
a
# => true

a = false or true
# => true
a
# => false

This is because it's actually interpreted as:

(a = false) or true

This is because = has a higher precedence when being evaluated.

What is the difference between '&&' and '&' in Ruby

&& is a boolean and. It returns the second argument if the first argument is true-ish. Because 0 is true-ish in Ruby, 1 is returned.

& is a bitwise and. It compares the bit representation of the values. Because (imaging 8 bit) 00000000 (0) and 00000001 (1) have no 1 digits in common, 00000000 (0) is returned.

What is the difference between %= ... % and % ... % in Ruby on Rails

This is ERB templating markup (one of many templating languages supported by Rails). This markup:

<% ... %>

is used to evaluate a Ruby expression. Nothing is done with the result of that expression, however. By contrast, the markup:

<%= ... %>

does the same thing (runs whatever Ruby code is inside there) but it calls to_s on the result and replaces the markup with the resulting string.

In short:

<% just run code %>
<%= run code and output the result %>

For example:

<% unless @items.empty? %>
  <ul>
    <% @items.each do |item| %>
      <li><%= item.name %></li>
    <% end %>
  </ul> 
<% end %>

In contrast, here's some Haml markup equivalent to the above:

- unless @items.empty?
  %ul
    - @items.each do |item|
      %li= item.name

What is the difference between :to and = in rails

In context of Rails routes:

• Is there a difference between these two statements?

There is no difference.

• If so why is one better than the other?

No, it's the same.

• Why is the rails community switching to the ":" notation (or are
  they)?

Just a more readable, 'from' => 'to' and 'from', to: 'to'

• Moving forward with rails 4 and soon 5, are both formats still
  acceptable?

Yes.

The => notation it's a hash ruby feature, and related to the :symbol.
You can write symbols by two ways :key => value and key: value.

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