Why is this an issue?
A common code smell that can hinder the clarity of source code is making assignments within sub-expressions. This practice involves assigning a value to a variable inside a larger expression, such as within a loop or a conditional statement.
This practice essentially gives a side-effect to a larger expression, thus making it less readable. This often leads to confusion and potential errors.
Exceptions
Assignments inside lambda and delegate expressions are allowed.
var result = Foo(() =>
{
int x = 100; // dead store, but ignored
x = 200;
return x;
}
The rule also ignores the following patterns:
- Chained assignments
var a = b = c = 10;
- Assignments that are part of a condition of an
ifstatement or a loop
while ((val = GetNewValue()) > 0)
{
...
}
- Assignment in the right-hand side of a coalescing operator
private MyClass instance;
public MyClass Instance => instance ?? (instance = new MyClass());
How to fix it
Making assignments within sub-expressions can hinder the clarity of source code.
This practice essentially gives a side-effect to a larger expression, thus making it less readable. This often leads to confusion and potential errors.
Extracting assignments into separate statements is encouraged to keep the code clear and straightforward.
Code examples
Noncompliant code example
if (string.IsNullOrEmpty(result = str.Substring(index, length))) // Noncompliant
{
// do something with "result"
}
Compliant solution
var result = str.Substring(index, length);
if (string.IsNullOrEmpty(result))
{
// do something with "result"
}