CODEWITHSUNDEEP
ruby
Joe Half Face
Joe Half Face

Reputation: 2333

What happens with further conditions if first one is `false`?

I often face the situation when if condition A (for example [email protected]?) is false, condition B, when checked, can raise an error (for example @object.some_method -> undefined method 'some_method' for nil:NilClass).

I tested it in console, but could't get some full data.

1) Is it safe to use and/&& when if first conditional is false, second can lead into an error?

2) What about or?

Upvotes: 0

Views: 62

Answers (2)

Thomas
Thomas

Reputation: 1633

Second part of these lines will never be exected:

false && raise "this will never be raised"
true || raise "this will never be raised"

In your case, if you are using active support, you can do:

@object.try!(:some_method)

Upvotes: 1

user513951
user513951

Reputation: 13690

[email protected]? && @object.some_method

@object && @object.some_method

Both of the above are valid patterns in Ruby. You will not get the "undefined method for nil" error, because the expression to the right of the && is never evaluated if the expression to the left of it evaluates to nil (or false).

You can also accomplish this check using postfix if or unless: 

@object.some_method if @object

or

@object.some_method unless @object.nil?

are both valid alternatives.

Regarding or:

Using || (Rubyists generally avoid the keyword or operator) will not protect you from the error, because when the expression on the left side of the || evaluates to nil, the interpreter will actually continue on and attempt to evaluate the expression on the right side.

Upvotes: 2

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