Avoid memory leak from creating temporary objects

Question

In Beef, I can have this code:

using System;

namespace Program
{
    class Foobar 
    {
        public int value;

        public this(int val)
        {
            value = val;
        }

        public static Foobar operator+(Foobar lhs, Foobar rhs)
        {
            let result = new Foobar();
            result.value = lhs.value + rhs.value;
            return result;
        }
    }

    class Program
    {
        public static void Main()
        {
            Foobar a = scope:: Foobar(5);
            Foobar b = scope:: Foobar(5);

            Foobar c = a + b;
            defer delete c;

            Console.Write("{}", c.value);

            Console.In.Read();

        }
    }
}

and that works fine, because I can easily delete the heap allocation made by the a+b operation. However, if I have:

using System;

namespace Program
{
    class Foobar 
    {
        public int value;

        public this(int val)
        {
            value = val;
        }

        public static Foobar operator+(Foobar lhs, Foobar rhs)
        {
            let result = new Foobar();
            result.value = lhs.value + rhs.value;
            return result;
        }
    }

    class Program
    {
        public static void Main()
        {
            Foobar a = scope:: Foobar(5);
            Foobar b = scope:: Foobar(5);
            Foobar x = scope:: Foobar(20);

            // Foobar c = (a + b) + x; // would leak

            Foobar temp = a + b;
            defer delete temp;

            Foobar c = temp + x;
            defer delete c;

            Console.Write("{}", c.value);
            Console.In.Read();

        }
    }
}

I have to do one addition at a time and delete each result one at a time.

Is there a better way to handle the destruction of these temporary variables?

Answer 1

The first thing I thought of was using a mixin which seems like the perfect solution however it doesn't support operators.

One other alternative is to wrap the result in a struct then implicitly cast back the struct to FooBar. The idea is that we need an intermediate struct to handle everything on the stack.

class Foobar {
    public int value;

    public this(int val) {
        value = val;
    }

    public static TempFoobar operator+(Foobar lhs, Foobar rhs) {
        let result = new Foobar(lhs.value + rhs.value);
        return TempFoobar(result);
    }
}

struct TempFoobar {
    Foobar result;
    public this(Foobar val) {
        result = val;
    }

    public void Replace(Foobar val) mut {
        delete result;
        result = val;
    }

    public static TempFoobar operator+(TempFoobar lhs, Foobar rhs) {
        var copy = lhs;
        let result = new Foobar(lhs.result.value + rhs.value);
        copy.Replace(result);
        return copy;
    }

    public static implicit operator Foobar(TempFoobar temp) {
         return temp.result;
    }
}


class Program {
    static mixin Add(Foobar lhs, Foobar rhs) {
        let result = scope:mixin Foobar(lhs.value + rhs.value);
        result
    }

    public static void Main() {
        Test();
        Console.In.Read();
    }

    public static void Test() {
        Foobar a = scope Foobar(5);
        Foobar b = scope Foobar(5);
        Foobar x = scope Foobar(20);
        //let c = Add!(Add!(a, b), x); //Mixin version
        Foobar c = (a + b) + x;
        defer delete c;
        Console.Write("{}", c.value);
    }
}

Granted, I would avoid operator overloading unless it really.. reallyyy makes sense, and would never return a heap instance from a function without a keyword such as 'create' or 'new' in the function name.

Side note, in this specific case you can just use an int as an intermediate object

    public static int operator+(Foobar lhs, Foobar rhs)
    {
        return lhs.value + rhs.value;
    }

    public static int operator+(int lhs, Foobar rhs)
    {
        return lhs + rhs.value;
    }

    public static implicit operator Foobar(int temp) {
         return new Foobar(temp);
    }

Again, I don't recommend doing this.

Answer 2

The best solution I can think of is to change it from a class to a struct. I'm not sure how to go about keeping Foobar as a class and still make this happen:

using System;

namespace Program
{
    struct Foobar 
    {
        public int value;

        public this(int val)
        {
            value = val;
        }

        public static Foobar operator+(Foobar lhs, Foobar rhs)
        {
            return Foobar(lhs.value + rhs.value);
        }
    }

    class Program
    {
        public static void Main()
        {
            Foobar a = Foobar(5);
            Foobar b = Foobar(5);
            Foobar x = Foobar(20);

            Foobar c = (a + b) + x; 

            Console.Write("{}", c.value);
            Console.In.Read();

        }
    }
}