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c#structstackreturn
Stefan B
Stefan B

Reputation: 541

C# return struct reference from method

In C++, returning a reference of an object allocated on the stack in a method, yields garbage values due to the fact, that the stack object is destroyed as soon the method leaves the scope. Given that in C# structs are allocated on the stack, would this yield garbage values as well?

struct Test
{
    //data
}

Test Foo()
{
    Test t1 = new Test();
    return t1;
}

Upvotes: 1

Views: 9056

Answers (2)

Artavazd Balayan
Artavazd Balayan

Reputation: 2413

keyword struct in C# describes a 'value type'. When you return a value type from a method, it creates new copy of it. Beware of shallow copies, should that structure contain embedded containers (such as List<T>, ...)

Upvotes: 1

JuanR
JuanR

Reputation: 7783

I think you should read this: http://mustoverride.com/ref-returns-and-locals/

In short, the C# Design team decided to disallow returning local variables by reference.

– Disallow returning local variables by reference. This is the solution that was chosen for C#. - To guarantee that a reference does not outlive the referenced variable C# does not allow returning references to local variables by reference. Interestingly, this is the same approach used by Rust, although for slightly different reasons. (Rust is a RAII language and actively destroys locals when exiting scopes)

Even with the ref keyword, if you go ahead and try this:

public struct Test
{
    public int a;
}

public ref Test GetValueByRef()
{
    var test = new Test();
    return ref test;
}

You will see that the compiler errors out with the following:

Cannot return local 'test' by reference because it is not a ref local

Upvotes: 2

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