How does string interpolation work without #{..} syntax?

Question

The code below is taken from page 118 of the Pickaxe book. Can someone explain to me why we do not need to do #{@name} to do interpolation?

class TaxCalculator
  def get_tax(amount)
    "#@name on #{amount} = #{@block.call(amount)}"
  end
end

Answer 1

When the expression to be interpolated is just a reference to a global, instance or class variable, then the braces can be omitted. The braces are only required for more complex expressions.

However, there is a debate about whether omitting the braces is a good idea from a style and readability perspective.

Answer 2

There is already a good answer to this question here:

Why does string interpolation work in Ruby when there are no curly braces?

In short: It's possible to spare the {} when you use a global, a class or an instance variable.