What is the purpose of setting Ruby block local variables when blocks have their own scope already?

Question

Learning about Ruby blocks here. What is the point of having block local variable in this example:

When you can just do the below instead? The x in the block is already going to have its own scope, which is different than the x that is outside the block.

Answer 1

Block scopes nest inside their lexically enclosing scope:

foo = :outerfoo
bar = :outerbar

1.times do |;bar|
  foo = :innerfoo
  bar = :innerbar
  baz = :innerbaz
end

foo #=> :innerfoo
bar #=> :outerbar
baz # NameError

You need a way to tell Ruby: "I don't want this variable from the outer scope, I want a fresh one." That's what block local variables do.

Answer 2

The point they're trying to make is that a block local variable (or a block parameter) will be completely separate from the variable outside of the block even if they have the same name, but if you just refer to x within the block without it being a block local variable or a block parameter, you're referring to the same x that exists outside the block.

They have this example right above the one you cite:

            x = 10
            5.times do |y|
              x = y
              puts "x inside the block: #{x}"
            end

            puts "x outside the block: #{x}"

Output:

            x inside the block: 0
            x inside the block: 1
            x inside the block: 2
            x inside the block: 3
            x inside the block: 4
            x outside the block: 4

Note that this is only the case if you refer to x before the block. If you removed the x = 10 line at the beginning, then the x in the block would be completely local to the block and that last line would error out (unless you had a method named x in the same object, in which case it would call that method).