Strange order of execution，There's no short circuit. What causes this？

[Arc-huangjingtong]

public class TestClass
{
    //change to int
    public static implicit operator int(TestClass c)
    {
        if (c == null)
        {
            throw new Exception();
        }

        return 1;
    }
}


public class Test
{
    public TestClass TestClass { get; set; }


    [Test]
    public void TestMethod()
    {
        int integer = false ? TestClass : default;

        Console.WriteLine(integer);//will throw Exception！
    }
}

[HaloFour]

With local type inference, the type of integer is TestClass, and the default value of TestClass is null.

var integer = false ? TestClass : default;

Did you mean?

int integer = false ? TestClass : default;

[Arc-huangjingtong]

thanks，but if you change “var”to “int” the exception is also throw

[HaloFour]

Yes, because you are trying to convert default of a TestClass to an int, and the conversion operator you have written will throw an exception in that case. The conversion takes place after the conditional operator expression.

[TahirAhmadov]

@Arc-huangjingtong it's a different exception - the one you throw in your implicit operator; the false ? TestClass : default is evaluated to null, then implicit operator is called with null and you have:

        if (c == null)
        {
            throw new Exception();
        }

[TahirAhmadov]

You want: int integer = false ? (int)TestClass : default;
Or try this even: int integer = false ? TestClass : 0; (i'm not sure if this works, though)

[Arc-huangjingtong]

yes ，you change “defualt” to 0，will works

[Arc-huangjingtong]

i want to know why not circuit？
this is not intuitive

[HaloFour]

The expression does short-circuit. That's not the problem. The issue is that the expression by itself is evaluated before the assignment, which is when the conversion operation occurs. The conditional expression false ? TestClass : default evaluates to a TestClass, not an int, and the default value of a TestClass is null.

[Arc-huangjingtong]

thanks， i see

[huoyaoyuan]

The tooltip can inform you that the default resolves to default(TestClass).