Blocks of statements in Ruby

Question

I have a background from languages which use {} to say that these are "block of statements" but i am learning ruby and really confused how it being done there.

So lets say in C i have

if ( condition )
{
  statement1;
  statement2;
}
else if (condition)
{
  statement1;
  statement2;

// nested if
       if (condition)
       {
          dosomethinghere;
       }
    }
    else
    {
      statement1;
      statement2;
    }

How i can put this code in ruby? and also mention how to understand synomenous of "{}" in ruby, thanks.

Answer 1

Well, to answer your first question:

if ( condition )
  statement1
  statement2
elsif (condition)
  statement1
  statement2
   // nested if
   if (condition)
     dosomethinghere
   end
else
  statement1
  statement2
end

The syntax rule for if statement is:

 if expr [then]
   expr...
[elsif expr [then]
    expr...]...
[else
   expr...]
 end

Where everything between [] is optional

However, and in other direction, you can also create and pass code blocks, check this post to read more about this topic.

Answer 2

The ruby syntax for if is:

if condition body else alternativa body end

Or

if condition then body else alternative body end

It's the same for while loops except with do instead of then.

{ and } are used to pass anonymous functions (confusingly called "blocks" in ruby) as arguments to methods.

Answer 3

in Ruby, the opening brace is implied after an if. to close the block, you use an end instead of a close brace. the only other difference is you use elsif (condition) instead of else if (condition).

Answer 4

If you're thinking "how do I create a new variable scope in Ruby"? ie:

{
    var myvar = 1;
}
myvar = 2; // compile error because myvar isn't in this scope!

I'm not really sure how you would do that.

Answer 5

I'd suggest getting a decent book and sitting down and reading the first few chapters this should cover everything you asked here and a lot more. I'd suggest http://oreilly.com/catalog/9780596529864 although if you're trying to get something done really quick http://www.troubleshooters.com/codecorn/ruby/basictutorial.htm is quite a good brief intro to get you started.

Answer 6

If you want a scope you can define your own scope method:

def scope
    yield
end

# use like this
scope {
    x = 5
    puts x #=> 5
}

x #=> undefined local variable

EDIT: for a better approach to 'scopes' in Ruby 1.9 see: http://banisterfiend.wordpress.com/2010/01/07/controlling-object-scope-in-ruby-1-9/

Answer 7

try running the following:

def example(x,y)

puts "X:#{x},Y:#{y}"

if ( x == 0 ) then
  puts "Its true"
elsif (x == 1)
  puts "Its not true"
  puts "it certainly isn't"
    if (y == 0) then
      puts "i'm the nested if"
    end
else
  puts "i made it to the default case"
  puts "freedom"
end
  puts 
end


example(0,0)
example(1,0)
example(1,1)
example(2,2)