Problem passing a structure by reference

zequion 211 Reputation points

I have a class and in one of the functions Fcn_Task_Async() I have a parameter that is a structure called "ref StTask_Async".

Inside the function, I need to create a Task passing "ref StTask_Async" to assign values ​​in the Fcn_Task_Async_Step2() function. However, Startnew does not allow me to use "ref StTask_Async" because it shows the error "CS1628: Cannot use in ref or out parameter inside an anonymous method, lambda expression, or query expression" and that forces me to use Name_Task_Async.St_Task_Async StTask_Async_ = StTask_Async ; to be able to pass "ref StTask_Async_".

My question: The strange thing is that, in the return, "StTask_Async" has the correct values ​​assigned to "StTask_Async_". I don't understand.

private Fcn_Task_Async(ref Name_Task_Async.St_Task_Async StTask_Async)


// Startnew forces me to use a local variable

Name_Task_Async.St_Task_Async StTask_Async_ = StTask_Async;

// Runs the task where it assigns variables to the local structure

StTask_Async.StTask_Async_Tasks[Task_index_].Task = System.Threading.Tasks.Task.Factory.StartNew<Name_Task_Async.St_Task_Async_Task>(() => Name_Task_AsyncAdd.Cls_Task_AsyncAdd.Fcn_Task_Async_Step2(ref StTask_Async_);

// Wait for StartNew completion.


// AT THIS POINT, if I query the values ​​​​of "StTask_Async" they are those assigned in the Task to the local structure. Why?


An object-oriented and type-safe programming language that has its roots in the C family of languages and includes support for component-oriented programming.
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  1. Jiale Xue - MSFT 42,321 Reputation points Microsoft Vendor

    Hi @zequion , Welcome to Microsoft Q&A,

    The behavior you observe is due to the way value types (such as structures) and reference types (such as classes) are handled in C#. When you pass a structure by value, you are passing a copy of the structure. However, when you pass a structure by reference (using ref), you are passing a reference to the original structure, allowing modifications to affect the original structure.

    private void Fcn_Task_Async(ref Name_Task_Async.St_Task_Async StTask_Async)
        // Create a local copy of the original struct
        Name_Task_Async.St_Task_Async StTask_Async_ = StTask_Async;
        // Start a new Task to modify the local copy
        StTask_Async.StTask_Async_Tasks[Task_index_].Task = System.Threading.Tasks.Task.Factory.StartNew(() =>
            Name_Task_AsyncAdd.Cls_Task_AsyncAdd.Fcn_Task_Async_Step2(ref StTask_Async_);
        // Wait for the Task to complete
        // After the Task completes, assign the modified local copy back to the original struct
        StTask_Async = StTask_Async_;

    Best Regards,


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