Why can't readonly be used with properties

Question

Why properties in C# cannot be readonly ?

When I try to have a property readonly it states that:

a modifier 'readonly' is not valid for this item

Simmilar question was asked here: Why can't properties be readonly? But the question was asked 5 years ago, and the answer provided then was: Because they didn't think it thru. Is this still the case after 5 years?

edit: Code example:

public class GreetingClass
{
    public readonly string HelloText { get; set; }
}

Well, technically nothing changed after that 5 years, and all answers to question you've mentioned are still up to date. — Andrey Korneyev, Dec 10 '15 at 07:38
Well, *property* is just a convenient name for `get`/`set` accessors which a *methods*. — Dmitry Bychenko, Dec 10 '15 at 07:45
See my answer. It compares C# 6.0 and prior versions. Things have changed a bit in C# 6.0. — Nikhil Vartak, Dec 10 '15 at 07:50

quadroid · Accepted Answer · 2018-08-17T09:50:58.697

Properties can be readonly in C#, the implementation is just not using the readonly keyword:

If you use C#6 (VS 2015) you can use the following line, which allows assigning the property in either the constructor or in the member definition.

public int Property { get; }

If you use an older C# / Visual Studio Version you can write something like this, and assign the field in the constructor or the field definition:

private readonly int property;
public int Property { get { return this.property; }}

score 7 · Answer 2 · edited Aug 16 '18 at 20:48

7

If you want to keep properties read only, you may just define their getter like this:

public MyProperty { get; }

edited Aug 16 '18 at 20:48

AustinWBryan

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answered Dec 10 '15 at 07:39

Ovais Khatri

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does this work for all C# versions or only for C#6+ ? – Stralos Dec 10 '15 at 07:42
it will work for all later than 2.0 – Ovais Khatri Dec 10 '15 at 07:53

sujith karivelil · Answer 3 · 2019-07-17T14:05:06.630

4

A property without set considered as a read-only property in C#, you need not specify them with a Readonly keyword.

public class GreetingClass
{
    private string _HelloText = "some text"; 
    public string HelloText => _HelloText; 
}

Whereas in VB you have to specify: Public ReadOnly Property HelloText() As String

edited Jul 17 '19 at 14:05

answered Dec 10 '15 at 07:39

sujith karivelil

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Can return value through private variable; see updates in the anser – sujith karivelil Dec 10 '15 at 07:46

MakePeaceGreatAgain · Answer 4 · 2018-08-20T08:54:41.667

0

More or less, from C#6 it s possible using something like this:

class MyClass {
    string MyProp { get; }
    MyClass { MyProp = "Hallo Worls"; }
}

Before C#6 you can use a read-only backing-field instead:

class MyClass {
    private readonly string _myProp;
    string MyProp { get { return this._myProp; } }
    MyClass { this._myProp = "Hallo Worls"; }
}

edited Aug 20 '18 at 08:54

answered Dec 10 '15 at 07:41

MakePeaceGreatAgain

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score 0 · Answer 5 · answered Dec 10 '15 at 07:49

If you had googled readonly properties in C#, you would have got 100*no_of_answers_here correct results.

https://msdn.microsoft.com/en-us/library/w86s7x04.aspx clearly states, a property without set accessor is readonly. So it's logical to think that applying readonly keyword in addition would cause redundancy, nothing else.

Additionally until C# 6.0 you could not set the readonly property even withing the containing type (say, a class). In C# 6.0, you can at least do so as a part of initialization. Meaning this is possible in C# 6.0, public int Prop { get; } = 10; When you do so, a readonly backing field is automatically generated and set to the value you chose for property initialization.

Why can't readonly be used with properties

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