Do I need to initobj/assign null to out arguments before ldloca and call?

Question

As I see C# compiler and Reflection.Emit always emits .locals init for both value and reference type variables (even if they are later unconditionally initialized). So they can be passed as an out argument:

    .maxstack 1
    .locals init (
        [0] object x)
    L_0000: ldloca.s x
    L_0002: call void Program::MethodWithOut(object&)
    L_0007: ret 

Are there any cases where .locals is used without init so before emitting call/callvirt I need to ensure the variable is initialized?

Answer 1

The simple answer is that init is always required to make the code verifiable. From §III.1.8.1.1 Verification algorithm of ECMA-335:

Furthermore, verifiable methods shall have the localsinit bit set […]. If this bit is not set, then a CLI might throw a Verification exception at any point where a local variable is accessed, and where the assembly containing that method has not been granted SecurityPermission.SkipVerification.

Answer 2

When your are passing parameters by ref you need to initialize them before passing. When you are passing parameters by out they must be initialized inside the called method.