https-github.com-gSchool-ruby-intro-to-enumerable-part-a

Class Notes:

Expressions and Statements:

What is an expression?

Any piece of code that evaluates to a value, this includes:

values - 7, "thing"
constants - ENV
variables - x, foo
operators - +, <<, *
functions - exit, puts

What is a statement?

A statement is a group of expressions to be carried out (or executed). Some examples:

assignment (and reassignment) statment - x = 8
return statement - return true
function (or method) call statement - exit()

We will use the term statement exclusively when talking about code, since we are primarily interested in action and not theory.

Note: Programs are just groups of statements.

Code Evaluation

We can say that code is evaluated when every statement is reduced to a value, and no expressions remain. For example:

"Sometimes the greatest writers,  " + " are not writers at all," + "but monkeys with typewriters."

evaluates to:

"Sometimes the greatest writers,   are not writers at all,but monkeys with typewriters."

Another example:

1 + 2 + 3 + 4 + 5

evaluates to:

Remember `.to_s`?

What is a receiver?

Suppose we have the following class:

class Foo
  def only_method
    puts "also best method! duh!"
  end
end

And the following code that uses this class:

foo = Foo.new # uses the implicit constructor provided by Ruby
foo.only_method
# => "also best method! duh!"

In this case foo, the object, is an instance of Foo, the class. When the instance method, only_method is called: foo.only_method it is said that foo is the receiver of the method call.

Getting back to .to_s

.to_s is a method that returns the String representation of the receiver
- it is defined on EVERY object (even nil!!!)
- can be thought of as "to String" (it is .toString() in many languages including Java, JavaScript, and Scala)

etmoore/ruby-intro-to-enumerable-part-a