Question

I want to enforce on my code base immutable rule with following test

[TestFixture]
public class TestEntityIf
{
    [Test]
    public void IsImmutable()
    {
        var setterCount =
            (from s in typeof (Entity).GetProperties(BindingFlags.Public | BindingFlags.Instance)
             where s.CanWrite
             select s)
                .Count();

        Assert.That(setterCount == 0, Is.True, "Immutable rule is broken");
    }
}

It passes for:

public class Entity
{
    private int ID1;
    public int ID
    {
        get { return ID1; }
    }
}

but doesn’t for this:

public class Entity
{
    public int ID { get; private set; }
}

And here goes the question “WTF?”

Answer 1

A small modification to answers posted elsewhere. The following will return non-zero if there is at least one property with a protected or public setter. Note the check for GetSetMethod returning null (no setter) and the test for IsPrivate (i.e. not public or protected) rather than IsPublic (public only).

    var setterCount =
           (from s in typeof(Entity).GetProperties(
              BindingFlags.Public
              | BindingFlags.NonPublic
              | BindingFlags.Instance)
            where
              s.GetSetMethod(true) != null // setter available
              && (!s.GetSetMethod(true).IsPrivate)
            select s).Count();

Nevertheless, as pointed out in Daniel Brückner’s answer, the fact that a class has no publicly-visible property setters is a necessary, but not a sufficient condition for the class to be considered immutable.