C#•2y ago

❔ Can someone help me fully understand ref returns?

I have not been able to get this through my head aside from a few things like never using a ref return if a variable does not exist outside of scope. What about something like keeping local variables alive through ref returns? Seeing the Span<T> type do these things confuses me. How is it able to do something like this considering ref return constraints, knowing it's a ref struct only on the stack? It's local but the GC knows it's still in use after returning

    public static Span<int> SpanOf(int[] arr)
    {
        var span = new Span<int>(arr);
        return span;
    }

    public static Span<int> SpanOf(int[] arr)
    {
        var span = new Span<int>(arr);
        return span;
    }

But you can't do anything like this which is what confuses me about the whole thing:

    public static ref int RefCopyOf(int n)
    {
        ref var refCopyOfN = ref n;
        return ref refCopyOfN;
    }

    public static ref int RefCopyOf(int n)
    {
        ref var refCopyOfN = ref n;
        return ref refCopyOfN;
    }

7 Replies

TheRanger•2y ago

local variables gets deleted when the program exits the method

Aaron•2y ago

so, that span example isn't getting a ref to the array local it's getting a ref to the first item of the array, which is on the heap which has a lifetime longer than your method so it's fine to return

Anton•2y ago

You can do the second thing if you pass that n as ref

uselessxp•2y ago

is there a way, a tool, to see what happens to variables and other stuffs during the debug, or you have just know it by theory?

deem•2y ago

Debug > Windows > Locals

Anton•2y ago

debugger

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ Can someone help me fully understand ref returns?