Why using the equality sign in an assignment of a constant?

Question

I have a question concerning constants in eiffel. Well it's just a semantic issue but it has been bugging me for some time now and I just don't understand the concept of this speciality.

For a normal assignment you use := which makes total sense in a mathematical thinking because it's the mathematical sign for an assignment

But if we look at the definition of a constant:

feature
    some_constant: INTEGER = 5

I just don't see why we use the equality sign there. Is there a certain reason? I would understand it the following way: We assign the value 5 to the constant but then why the boolean expression?

I hope someone can explain the concept behind this

Answer 1

You have to treat the = sign as a quick contract for the constant feature.

foo: INTEGER = 5

would be identical to

foo: INTEGER
  ensure
    Result = 5

Note that this is a recent syntax change, before it used to be

foo: INTEGER is 5

but the Eiffel specification dropped the is keyword altogether.