S3240 — The simplest possible condition syntax should be used

Why is this an issue?

In the interests of keeping code clean, the simplest possible conditional syntax should be used. That means

• using the ??= operator for a self-assign-if-not-null operation,
• using the ?? operator for an assign-if-not-null operation, and
• using the ternary operator ?: for assignment to a single variable.

Noncompliant code example

object a = null, b = null, x;

if (a != null) // Noncompliant; needlessly verbose
{
  x = a;
}
else
{
  x = b;
}

x = a != null ? a : b; // Noncompliant; better but could still be simplified

x = (a == null) ? new object() : a; // Noncompliant

if (condition) // Noncompliant
{
  x = a;
}
else
{
  x = b;
}

if (a == null)  // Noncompliant
    a = new object();

var y = null ?? new object(); // Noncompliant

a = a ?? new object();  // Noncompliant for C# 8

Compliant solution

object x;

x = a ?? b;
x = a ?? b;
x = a ?? new object();
x = condition ? a : b;
a ??= new object();
var y = new object();
a ??= new object();