Member Avatar for Tellalca

Hey,

I am developing a game in C#. I have some question marks in my mind about properties.

-Should I return reference in a get, or should I clone the reference and return a clone?

If I return a reference then in another part of the program, it will be possible to get that reference from get, copy it to another object and modify it, it is bad isn't it?

If I return a clone, then I need to use the private field itself in the class implementing the property, it is bad too isn't it?

What are the best practices about using properties in C#?

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  • Latest Post Latest Post by Narue

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Short answer: pick an ownership contract and make it explicit. There are three practical choices: share the same instance (caller and owner both reference the object), take ownership by copying on set, or return a defensive copy on get. Each has trade‑offs: sharing is fastest but lets callers mutate your state; copying prevents aliasing but costs time and allocations; immutability avoids both problems when it’s feasible.

Design guidelines that help decide:

  • Treat properties as field-like: quick, predictable, and free of surprising allocations or side effects. If returning a clone would be expensive or nontrivial, expose a clearly named method (for example, GetCopy or CreateCopy) instead of hiding that work in a getter.
  • Prefer explicit copy APIs (copy constructor or a Copy/With method) rather than ICloneable; the latter is ambiguous about shallow vs deep copying.
  • For collections, prefer read-only interfaces or immutable collections instead of returning the internal list and hoping callers don’t mutate it.

Practical notes for implementation and construction:

  • If the setter enforces invariants or raises events, centralize that logic in a private helper you can call from both the setter and the constructor so you don’t accidentally bypass important checks. Conversely, if the ctor truly owns initial state and no invariants apply yet, assigning the backing field directly is acceptable.
  • Document ownership clearly: callers must know whether they may mutate a returned object or whether they should request a copy. Also measure performance if you do cloning frequently (games often favor minimizing allocations).

Checklist: decide ownership intent; prefer immutability where possible; avoid expensive clones in property getters (use methods instead); use explicit copy APIs and document the contract. This frames the tradeoffs is weighing and complements ’s point about cloning only when aliasing is a real problem.

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Member Avatar for Narue

What are the best practices about using properties in C#?

Best practice is really no different from parameters and return values from functions. If you can get away with a reference, do so. It's generally more efficient for both space and execution time. Not to mention that it's easier to reason about a single object's lifetime than multiple copies of the object.

Member Avatar for Tellalca

Best practice is really no different from parameters and return values from functions. If you can get away with a reference, do so. It's generally more efficient for both space and execution time. Not to mention that it's easier to reason about a single object's lifetime than multiple copies of the object.

Hi Narue, nice new avatar.

Can you please give some examples?

Member Avatar for Narue

Can you please give some examples?

Examples of what?

Member Avatar for Tellalca

Examples of how do you handle returning references by properties?

Do you just return the reference or return the clone?

If you return the clone, how do you handle assignments to the reference while implementing the class methods without loosing implemented set/get logic in a property?

If you return the reference, how do you make sure that reference will not be modified by external calls?

class Car
    {
        private Engine _engine;

        public Engine Engine
        {
            get { return _engine.Clone(); }
            set
            {
                if(value.HP > 200)
                {
                    throw new Exception("Too much power for the current car model!");
                }

                _engine = value.Clone();
            }
        }

        public Car()
        {
            // Use property to ensure property logic runs
            Engine = new Engine(400); // Edit: OK, set to the clone of the value

            // Use reference but loose the property logic, loose events in the property too
            _engine = new Engine(400); // This one bypasses the 200 HP limit in the property logic
        }
    }
Edited by Tellalca because: n/a
Member Avatar for Tellalca

OK, I think I got it.

When setting, I should set to the clone of the value so that any modify to the value will not affect our reference later.

When getting, I should simply return the clone if it is a reference type.

Member Avatar for Narue

Examples of how do you handle returning references by properties?

Do you just return the reference or return the clone?

There's no cloning going on:

class Car {
    private Engine _engine;
    public Engine Engine {
        get { return _engine; }
        set {
            if (value.HP > 200)
                throw new ArgumentException("Horsepower too high for car model");

            _engine = value;
        }
    }

    public Car() {
        Engine = new Engine(400);
    }
}

If you're worried about aliases then you can clone on the set of your property:

set {
    // ...
    _engine = value.Clone();
}

But I'd ask for a use case that actually fails due to aliasing, otherwise you're making an unnecessary clone.

The horsepower check is a little odd as well. That doesn't seem like the place it should be to me. The restriction for placing an engine in a car really has nothing to do with horsepower. In fact, unless you're supporting some sort of feature for non-stock engine swaps, it would be best to base the engine on the model and not expose a public set at all:

abstract class Car {
    public Engine Engine { get; protected set; }
}

class SomeSpecificModel: Car {
    public SomeSpecificModel() {
        Engine = new Engine(400);
    }
}

Now the horsepower is a non-issue because it's assumed to be stock, and you can use an auto-property.

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