Recursive call to operator==¶
ID: cs/recursive-operator-equals-call
Kind: problem
Security severity:
Severity: error
Precision: medium
Tags:
- reliability
- maintainability
Query suites:
- csharp-security-and-quality.qls
Click to see the query in the CodeQL repository
When writing an operator==, it is common to want to check whether or not an operand is null or check if both operands refer to the same object. Attempting to do this using == will not work as it will simply call the overridden operator== that is being defined.
Recommendation¶
There are two suggested ways to fix the problem. The tidiest approach is to simply replace the call to operator== with a call to ReferenceEquals (see code below). As a less preferable alternative, it is also possible to simply cast the parameters to object .
Example¶
In this example the == overload will constantly call itself to compare the initial arguments passed to it with null.
class Year
{
private int year;
private bool bc;
public Year(int i)
{
year = Math.Abs(i);
bc = i < 0;
}
public static bool operator ==(Year lhs, Year rhs)
{
// Both of these checks against null call operator== recursively.
// They were probably intended to be checks for reference equality.
if (lhs == null || rhs == null)
{
return false;
}
return lhs.year == rhs.year && lhs.bc == rhs.bc;
}
public static bool operator !=(Year lhs, Year rhs)
{
return !(lhs == rhs);
}
}
The best fix is to use the ReferenceEquals method instead.
class Year
{
private int year;
private bool bc;
public Year(int i)
{
year = Math.Abs(i);
bc = i < 0;
}
public static bool operator ==(Year lhs, Year rhs)
{
// Either of these alternative approaches works.
if (ReferenceEquals(lhs, null) || (object)rhs == null)
{
return false;
}
return lhs.year == rhs.year && lhs.bc == rhs.bc;
}
public static bool operator !=(Year lhs, Year rhs)
{
return !(lhs == rhs);
}
}