Overview¶

ID: rb/uninitialized-local-variable
Kind: problem
Security severity: 
Severity: error
Precision: high
Tags:
   - quality
   - reliability
   - correctness
Query suites:
   - ruby-security-and-quality.qls

Click to see the query in the CodeQL repository

In Ruby, it is not necessary to explicitly initialize variables. If a local variable has not been explicitly initialized, it will have the value nil. If this happens unintentionally, though, the variable will not represent an object with the expected methods, and a method call on the variable will raise a NoMethodError.

Recommendation¶

Ensure that the variable cannot be nil at the point highlighted by the alert. This can be achieved by using a safe navigation or adding a check for nil.

Note: You do not need to explicitly initialize the variable, if you can make the program deal with the possible nil value. In particular, initializing the variable to nil will have no effect, as this is already the value of the variable. If nil is the only possible default value, you need to handle the nil value instead of initializing the variable.

Example¶

def dump(x)
  f = create_file
  f.puts(x)
ensure
  f.close
end

def dump(x)
  f = create_file
  f.puts(x)
ensure
  f&.close
end

References¶

• RubyGuides: Everything You Need To Know About Nil.

• Ruby-Doc.org: NoMethodError.