C#•5mo ago

✅ A nicer way to create an on-demand property?

Is there a nicer way to create sum here?

Foo f = new() {
    X = 3,
    Y = 4
};

f.Dump();

class Foo
{
    public required int X { get; init; }
    public required int Y { get; init; }
    private int? sum = null;

    public int Sum
    {
        get
        {
            Console.WriteLine("Calculating Sum");
            sum ??= X + Y;
            return sum.Value;
        }
    }
}

Foo f = new() {
    X = 3,
    Y = 4
};

f.Dump();

class Foo
{
    public required int X { get; init; }
    public required int Y { get; init; }
    private int? sum = null;

    public int Sum
    {
        get
        {
            Console.WriteLine("Calculating Sum");
            sum ??= X + Y;
            return sum.Value;
        }
    }
}

7 Replies

Jason_BjornOP•5mo ago

I was thinking about using Lazy but that doesn't seem to clean thing up

Foo f = new()
{
    X = 3,
    Y = 4
};

f.Dump();

class Foo
{
    public required int X { get; init; }
    public required int Y { get; init; }
    private int? sum = null;

    public int Sum
    {
        get
        {
            Console.WriteLine("Calculating Sum");
            sum ??= X + Y;
            return sum.Value;
        }
    }

    private Lazy<int> bum; // no longer needs to be int? which is nice
    public int Bum // getter no longer needs to worry about the logic behind the value of bum, which is nice
    {
        get
        {
            return bum.Value;
        }
    }

    public Foo() // constructor needed to let Bum know how to get the value of bum
    {
        bum = new Lazy<int>(() =>
        {
            Console.WriteLine("Calculating Bum");
            return X + Y;
        });
    }
}

Foo f = new()
{
    X = 3,
    Y = 4
};

f.Dump();

class Foo
{
    public required int X { get; init; }
    public required int Y { get; init; }
    private int? sum = null;

    public int Sum
    {
        get
        {
            Console.WriteLine("Calculating Sum");
            sum ??= X + Y;
            return sum.Value;
        }
    }

    private Lazy<int> bum; // no longer needs to be int? which is nice
    public int Bum // getter no longer needs to worry about the logic behind the value of bum, which is nice
    {
        get
        {
            return bum.Value;
        }
    }

    public Foo() // constructor needed to let Bum know how to get the value of bum
    {
        bum = new Lazy<int>(() =>
        {
            Console.WriteLine("Calculating Bum");
            return X + Y;
        });
    }
}

Is the bum approach better?

SleepWellPupper•5mo ago

You're trying to implement lazy behavior. So using Lazy seems generally like a good approach. Do you require thread safety? Do you not care about the extra allocation? Then Lazy will probably fit the bill. Nothing wrong with doing it manually either if your specific usecase doesn't suffer for it. There's no "better" approach to be recommended without more detail on your specific usecase imo In fact, in your specific sample code, I'd go for a manual implementation since the null check and factory are cheap plus the factory is side effect free and so concurrent execution is a non-issue.

Jason_BjornOP•5mo ago

putting the logic of initializing bum into the constructor just seems weird

SleepWellPupper•5mo ago

so use a field initializer private readonly Lazy<int> _lazySum = new(()=>X+Y); Or extract the factory delegate into a method.

Jason_BjornOP•5mo ago

field initializers cannot reference non-static properties

// method 3 using Lazy<int> and field initilizer
    private Lazy<int> tum = new Lazy<int>(() =>
    {
        Console.WriteLine("Calculating tum");
        return X + Y;
    });
    public int Tum
    {
        get
        {
            return tum.Value;
        }
    }

// method 3 using Lazy<int> and field initilizer
    private Lazy<int> tum = new Lazy<int>(() =>
    {
        Console.WriteLine("Calculating tum");
        return X + Y;
    });
    public int Tum
    {
        get
        {
            return tum.Value;
        }
    }

SleepWellPupper•5mo ago

right. Constructor it is, then :)

Jason_BjornOP•5mo ago

Thanks

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✅ A nicer way to create an on-demand property?