nj. nj. - 1 month ago 5
C# Question

Why does short-circuiting not prevent MissingMethodException related to unreachable branch of logical AND (&&)?

While performing a check if there's a camera present and enabled on my windows mobile unit I encountered something I don't understand.

The code looks like this:

public static bool CameraP(){

return Microsoft.WindowsMobile.Status.SystemState.CameraPresent;
}

public static bool CameraE()
{
return Microsoft.WindowsMobile.Status.SystemState.CameraEnabled;
}

public static bool CameraPresent1()
{
return Microsoft.WindowsMobile.Status.SystemState.CameraPresent
&& Microsoft.WindowsMobile.Status.SystemState.CameraEnabled;
}

public static bool CameraPresent2()
{
return CameraP() && CameraE();
}


When I call
CameraPresent2()
it return false (there is no camera present). But when I call
CameraPresent1()
i recieve a MissingMethodException with comment "Could not find method: get_CameraEnabled Microsoft.WindowsMobile.Status.SystemState."

Is the second term evaluated in
CameraPresent1
just because they both are property (at language level)?

Is there anything else that explains the difference in behaviour?

Answer

The second term is not evaluated.

The first term is not evaluated.

The CameraPresent1() method does not even start to execute.

When you call CameraPresent1() for the first time, the runtime must JIT-compile the MSIL into native code. This requires resolving all method calls, even ones that might be reached only conditionally. Compilation fails with the MissingMethodException.

With CameraPresent2(), the call to the getter of CameraEnabled is only compiled when CameraE() is called for the first time, which never happens.

Comments