What does the following warning mean: 'side-effecting nullary methods are discouraged'?

Question

I have a lot of nullary methods (methods with 0 parameters) in my scala test file. Hence, instead of writing them as :

def fooBar() = //

I write them as :

def fooBar = //

I get the following warning when I do so:

Warning:(22, 7) side-effecting nullary methods are discouraged: suggest defining as `def fooBar()` instead

What is the meaning of the warning? I am using intelliJ as my IDE and could not really find much about this warning on the web.

EDIT

And, I forgot to mention, when I use the brackets, the warning does not appear.

Answer 1

Does fooBar have side-effects?

It's simply stating a good practice to define a side-effecting method as such:

def fooBar() = ...

And non-side-effecting methods like this:

def fooBar = ...

Since the method call looks similar to accessing a val, it's good to differentiate when the method is doing more than just returning a value.

Answer 2

The common convention for nullary methods is to:

• in case it's a side-effecting method, signify it with use of parenthesis
• otherwise, drop parenthesis in case it's pure accessor-like method with no side effects

You're breaking this rule and IDE warns you about this.

See also https://stackoverflow.com/a/7606214/298389