Why is it desirable to use all properties instead of public instance variables in c#?

Question

I know properties have some advantages, but if you think you won't need a property, what's the harm in making it a public instance?

People say that changing the public field to a property will break code if you try to do it later on but in my experience changing it to a property breaks nothing.

Properties give you more control on the data parsed to your class, you don't want any old bit of data getting un-validated into your class and throwing exceptions. — Callum Linington, Jul 09 '13 at 09:01
What happens if you need to do some validation on the field before setting it? Or what happens when you want an event to be fired when the field changes? You can't do either of those easily with a field. There is no real performance penalty to using properties, as auto-implemented and small properties will be inlined by the JITter anyways. — Robert Rouhani, Jul 09 '13 at 09:01
Properties are also used in databinding, so u don't need to manual update your GUI. Great for MVC — DarkBee, Jul 09 '13 at 09:02
Changing to a property could cause [this error](http://stackoverflow.com/questions/1747654/cannot-modify-the-return-value-error-c-sharp). (I ama fan of properties however) — Sayse, Jul 09 '13 at 09:06
@Falanwe - Just pointing out changing to a property can break things :) — Sayse, Jul 09 '13 at 09:16

score 7 · Accepted Answer · answered Jul 09 '13 at 09:01

7

I think that people mean that it breaks ABI (binary) compatibility, not the API (source) compatibility.

Although the syntax is identical, behind the scenes, access to properties and access to member variables are compiled differently.

That said, if your variable/property is not to be used from an assembly that you yourself do not compile, then there is no harm in changing it. But if it is part of a public interface, then it is better to make it a property, so that you will not regret it in the future.

answered Jul 09 '13 at 09:01

rodrigo

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In what way are they different? – MoonKnight Jul 09 '13 at 09:02
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@Killercam: Access to a property is compiled as a method call. – Daniel Hilgarth Jul 09 '13 at 09:03
@Killercam see [description](http://csharpindepth.com/articles/chapter8/propertiesmatter.aspx) – Bob Vale Jul 09 '13 at 09:05
@Killercam: To read property `Foo` of type `T` the compiler calls a method `T get_Foo()` and to set it, it calls `void set_Foo(T value)`. – rodrigo Jul 09 '13 at 09:09

score 2 · Answer 2 · answered Jul 09 '13 at 10:06

It's about maintaining both binary and source compatibility. Some time in the future you may decide to make logic of assigning values more complex and to change fields to properties. This is where the problems emerge.

Public fields can be used as out and ref parameters. Properties cannot. This will produce uncompilable code.
Different Reflection methods are used to access fields and properties. That means any code that gets or sets values using Reflection will break, and you'll know about it only in run time.
Different IL operators are used to access fields and properties. That means cross-assembly compatibility is broken when fields are changed to properties and only one assembly is recompiled. This will make your program fail at run time.

score 0 · Answer 3 · answered Jul 09 '13 at 09:03

I concour with you, if the property is just a wrapper on the field. And the guys at Coding Horror looks like having our same opinion, I find very funny that frightened icon they use :) http://www.codinghorror.com/blog/2006/08/properties-vs-public-variables.html

score 0 · Answer 4 · answered Jul 09 '13 at 09:07

A simple program.

Here I am adding two properties and one variables. We can use properties as per our decision. But I prefer to use properties because it helps to implement some bussiness validation and can hide the business logic form calling party.

class Program
    {
        static void Main(string[] args)
        {
            Human h = new Human();
            h.FirstName = "Test";
            h.LastName = "User";
            Console.WriteLine(h.FullName);
            Console.Read();
        }
    }
    class Human
    {
        public string FullName { get { return FirstName + " " + LastName; } }
        public string FirstName;//{ get; set; }
        public string LastName;//{ get; set; }

    }

Why is it desirable to use all properties instead of public instance variables in c#?

4 Answers4