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Readonly vs static readonly clarification
2019 Community Moderator ElectionHow to properly access c++/CLI initonly TimeSpan field?What is the difference between const and readonly?Static readonly vs constWhy does Microsoft advise against readonly fields with mutable values?const, readonly and mutable value typesStruct containing reference typesConverting to int from string in public staticFilename pattern not working in OpenFileDialogStatic Readonly Fields and PerformanceMimicing constants using static readonly vs static getterStatic referenced in another .cs file
I've run into an interesting situation I am trying to understand. I have a readonly struct field in my class. This means that when I reference it, it references a copy and not the actual one, so when I call a change method, it will be working with a copy, and the original will remain unchanged.
That is not what I am observing. I only see the expected behavior with a static field. I expected the behavior for both types.
private struct junk
{
public int i;
public void change()
{
i += 1;
}
}
private readonly junk jk;
private static readonly junk jk2;
public Form1()
{
InitializeComponent();
jk.change();
//jk.i is now 1, why? Shouldn't it be changing a copy and not the original jk?
jk2.change();
//jk2.i is 0
}
c#
asked 4 hours ago
Endel_Endel_
361
New contributor
Endel_ is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
I've run into an interesting situation I am trying to understand. I have a readonly struct field in my class. This means that when I reference it, it references a copy and not the actual one, so when I call a change method, it will be working with a copy, and the original will remain unchanged.
That is not what I am observing. I only see the expected behavior with a static field. I expected the behavior for both types.
private struct junk
{
public int i;
public void change()
{
i += 1;
}
}
private readonly junk jk;
private static readonly junk jk2;
public Form1()
{
InitializeComponent();
jk.change();
//jk.i is now 1, why? Shouldn't it be changing a copy and not the original jk?
jk2.change();
//jk2.i is 0
}
c#
asked 4 hours ago
Endel_Endel_
361
New contributor
Endel_ is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
3
Mutable value types - just say no.
– Damien_The_Unbeliever
4 hours ago
1
please get rid of the irrelevant call toInitializeComponent()and insert code that prints the values ofjk.iandjk2.iand show us what it prints. We do not care to read what you think the values are, we want to see what the values are.
– Mike Nakis
4 hours ago
1
(And we also want to see what makes you think the values are what you claim they are.)
– Mike Nakis
4 hours ago
1
A warning would have been nice, but the C# compiler does not have the plumbing that can ensure that change() has an observable side-effect. A counter-example is the C++/CLI compiler, it always assumes and that doesn't make programmers happy either. Addstatic Form1()to see that it is allowed to mutate the jk2 value.
– Hans Passant
4 hours ago
add a comment |
I've run into an interesting situation I am trying to understand. I have a readonly struct field in my class. This means that when I reference it, it references a copy and not the actual one, so when I call a change method, it will be working with a copy, and the original will remain unchanged.
That is not what I am observing. I only see the expected behavior with a static field. I expected the behavior for both types.
private struct junk
{
public int i;
public void change()
{
i += 1;
}
}
private readonly junk jk;
private static readonly junk jk2;
public Form1()
{
InitializeComponent();
jk.change();
//jk.i is now 1, why? Shouldn't it be changing a copy and not the original jk?
jk2.change();
//jk2.i is 0
}
c#
asked 4 hours ago
Endel_Endel_
361
New contributor
Endel_ is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
I've run into an interesting situation I am trying to understand. I have a readonly struct field in my class. This means that when I reference it, it references a copy and not the actual one, so when I call a change method, it will be working with a copy, and the original will remain unchanged.
That is not what I am observing. I only see the expected behavior with a static field. I expected the behavior for both types.
private struct junk
{
public int i;
public void change()
{
i += 1;
}
}
private readonly junk jk;
private static readonly junk jk2;
public Form1()
{
InitializeComponent();
jk.change();
//jk.i is now 1, why? Shouldn't it be changing a copy and not the original jk?
jk2.change();
//jk2.i is 0
}
c#
c#
asked 4 hours ago
Endel_Endel_
361
New contributor
Endel_ is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 4 hours ago
Endel_Endel_
361
New contributor
Endel_ is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 4 hours ago
Endel_Endel_
361
New contributor
Endel_ is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 4 hours ago
Endel_Endel_
361
asked 4 hours ago
Endel_Endel_
361
361
New contributor
Endel_ is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Endel_ is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Endel_ is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
3
Mutable value types - just say no.
– Damien_The_Unbeliever
4 hours ago
1
please get rid of the irrelevant call toInitializeComponent()and insert code that prints the values ofjk.iandjk2.iand show us what it prints. We do not care to read what you think the values are, we want to see what the values are.
– Mike Nakis
4 hours ago
1
(And we also want to see what makes you think the values are what you claim they are.)
– Mike Nakis
4 hours ago
1
A warning would have been nice, but the C# compiler does not have the plumbing that can ensure that change() has an observable side-effect. A counter-example is the C++/CLI compiler, it always assumes and that doesn't make programmers happy either. Addstatic Form1()to see that it is allowed to mutate the jk2 value.
– Hans Passant
4 hours ago
add a comment |
3
Mutable value types - just say no.
– Damien_The_Unbeliever
4 hours ago
1
please get rid of the irrelevant call toInitializeComponent()and insert code that prints the values ofjk.iandjk2.iand show us what it prints. We do not care to read what you think the values are, we want to see what the values are.
– Mike Nakis
4 hours ago
1
(And we also want to see what makes you think the values are what you claim they are.)
– Mike Nakis
4 hours ago
1
A warning would have been nice, but the C# compiler does not have the plumbing that can ensure that change() has an observable side-effect. A counter-example is the C++/CLI compiler, it always assumes and that doesn't make programmers happy either. Addstatic Form1()to see that it is allowed to mutate the jk2 value.
– Hans Passant
4 hours ago
3
3
Mutable value types - just say no.
– Damien_The_Unbeliever
4 hours ago
Mutable value types - just say no.
– Damien_The_Unbeliever
4 hours ago
1
1
please get rid of the irrelevant call to
InitializeComponent() and insert code that prints the values of jk.i and jk2.i and show us what it prints. We do not care to read what you think the values are, we want to see what the values are.– Mike Nakis
4 hours ago
please get rid of the irrelevant call to
InitializeComponent() and insert code that prints the values of jk.i and jk2.i and show us what it prints. We do not care to read what you think the values are, we want to see what the values are.– Mike Nakis
4 hours ago
1
1
(And we also want to see what makes you think the values are what you claim they are.)
– Mike Nakis
4 hours ago
(And we also want to see what makes you think the values are what you claim they are.)
– Mike Nakis
4 hours ago
1
1
A warning would have been nice, but the C# compiler does not have the plumbing that can ensure that change() has an observable side-effect. A counter-example is the C++/CLI compiler, it always assumes and that doesn't make programmers happy either. Add
static Form1() to see that it is allowed to mutate the jk2 value.– Hans Passant
4 hours ago
A warning would have been nice, but the C# compiler does not have the plumbing that can ensure that change() has an observable side-effect. A counter-example is the C++/CLI compiler, it always assumes and that doesn't make programmers happy either. Add
static Form1() to see that it is allowed to mutate the jk2 value.– Hans Passant
4 hours ago
add a comment |
1 Answer
1
active
oldest
votes
I have a readonly struct field in my class. This means that when I reference it, it references a copy and not the actual one, so when I call a change method, it will be working with a copy, and the original will remain unchanged.
That's not at all what the readonly modifier does. The readonly modifier prevents you from assigning a new value to jk anywhere but in a constructor. Then, the static modifier allows you to reuse that value independently of the instance of Form1 you are working with.
That said, neither readonly nor static is making the weird behavior you are describing because that exact behavior cannot be reproduced with the code you've posted.
Look at a simpler example in a Console application (which you can try here):
public class Program
{
private readonly junk jk;
private static readonly junk jk2;
public static void Main()
{
var program = new Program();
program.jk.change();
Console.WriteLine(program.jk.i); // prints 0
jk2.change();
Console.WriteLine(jk2.i); // prints 0
}
}
public struct junk
{
public int i;
public void change()
{
i += 1;
}
}
Then, as @Damien_The_Unbeliever commented, try to avoid mutable structs as much as you can.
answered 4 hours ago
Camilo TerevintoCamilo Terevinto
19k63767
add a comment |
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I have a readonly struct field in my class. This means that when I reference it, it references a copy and not the actual one, so when I call a change method, it will be working with a copy, and the original will remain unchanged.
That's not at all what the readonly modifier does. The readonly modifier prevents you from assigning a new value to jk anywhere but in a constructor. Then, the static modifier allows you to reuse that value independently of the instance of Form1 you are working with.
That said, neither readonly nor static is making the weird behavior you are describing because that exact behavior cannot be reproduced with the code you've posted.
Look at a simpler example in a Console application (which you can try here):
public class Program
{
private readonly junk jk;
private static readonly junk jk2;
public static void Main()
{
var program = new Program();
program.jk.change();
Console.WriteLine(program.jk.i); // prints 0
jk2.change();
Console.WriteLine(jk2.i); // prints 0
}
}
public struct junk
{
public int i;
public void change()
{
i += 1;
}
}
Then, as @Damien_The_Unbeliever commented, try to avoid mutable structs as much as you can.
answered 4 hours ago
Camilo TerevintoCamilo Terevinto
19k63767
add a comment |
I have a readonly struct field in my class. This means that when I reference it, it references a copy and not the actual one, so when I call a change method, it will be working with a copy, and the original will remain unchanged.
That's not at all what the readonly modifier does. The readonly modifier prevents you from assigning a new value to jk anywhere but in a constructor. Then, the static modifier allows you to reuse that value independently of the instance of Form1 you are working with.
That said, neither readonly nor static is making the weird behavior you are describing because that exact behavior cannot be reproduced with the code you've posted.
Look at a simpler example in a Console application (which you can try here):
public class Program
{
private readonly junk jk;
private static readonly junk jk2;
public static void Main()
{
var program = new Program();
program.jk.change();
Console.WriteLine(program.jk.i); // prints 0
jk2.change();
Console.WriteLine(jk2.i); // prints 0
}
}
public struct junk
{
public int i;
public void change()
{
i += 1;
}
}
Then, as @Damien_The_Unbeliever commented, try to avoid mutable structs as much as you can.
answered 4 hours ago
Camilo TerevintoCamilo Terevinto
19k63767
add a comment |
I have a readonly struct field in my class. This means that when I reference it, it references a copy and not the actual one, so when I call a change method, it will be working with a copy, and the original will remain unchanged.
That's not at all what the readonly modifier does. The readonly modifier prevents you from assigning a new value to jk anywhere but in a constructor. Then, the static modifier allows you to reuse that value independently of the instance of Form1 you are working with.
That said, neither readonly nor static is making the weird behavior you are describing because that exact behavior cannot be reproduced with the code you've posted.
Look at a simpler example in a Console application (which you can try here):
public class Program
{
private readonly junk jk;
private static readonly junk jk2;
public static void Main()
{
var program = new Program();
program.jk.change();
Console.WriteLine(program.jk.i); // prints 0
jk2.change();
Console.WriteLine(jk2.i); // prints 0
}
}
public struct junk
{
public int i;
public void change()
{
i += 1;
}
}
Then, as @Damien_The_Unbeliever commented, try to avoid mutable structs as much as you can.
answered 4 hours ago
Camilo TerevintoCamilo Terevinto
19k63767
I have a readonly struct field in my class. This means that when I reference it, it references a copy and not the actual one, so when I call a change method, it will be working with a copy, and the original will remain unchanged.
That's not at all what the readonly modifier does. The readonly modifier prevents you from assigning a new value to jk anywhere but in a constructor. Then, the static modifier allows you to reuse that value independently of the instance of Form1 you are working with.
That said, neither readonly nor static is making the weird behavior you are describing because that exact behavior cannot be reproduced with the code you've posted.
Look at a simpler example in a Console application (which you can try here):
public class Program
{
private readonly junk jk;
private static readonly junk jk2;
public static void Main()
{
var program = new Program();
program.jk.change();
Console.WriteLine(program.jk.i); // prints 0
jk2.change();
Console.WriteLine(jk2.i); // prints 0
}
}
public struct junk
{
public int i;
public void change()
{
i += 1;
}
}
Then, as @Damien_The_Unbeliever commented, try to avoid mutable structs as much as you can.
answered 4 hours ago
Camilo TerevintoCamilo Terevinto
19k63767
answered 4 hours ago
Camilo TerevintoCamilo Terevinto
19k63767
answered 4 hours ago
Camilo TerevintoCamilo Terevinto
19k63767
answered 4 hours ago
Camilo TerevintoCamilo Terevinto
19k63767
19k63767
add a comment |
add a comment |
Endel_ is a new contributor. Be nice, and check out our Code of Conduct.
Endel_ is a new contributor. Be nice, and check out our Code of Conduct.
Endel_ is a new contributor. Be nice, and check out our Code of Conduct.
Endel_ is a new contributor. Be nice, and check out our Code of Conduct.
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3
Mutable value types - just say no.
– Damien_The_Unbeliever
4 hours ago
1
please get rid of the irrelevant call to
InitializeComponent()and insert code that prints the values ofjk.iandjk2.iand show us what it prints. We do not care to read what you think the values are, we want to see what the values are.– Mike Nakis
4 hours ago
1
(And we also want to see what makes you think the values are what you claim they are.)
– Mike Nakis
4 hours ago
1
A warning would have been nice, but the C# compiler does not have the plumbing that can ensure that change() has an observable side-effect. A counter-example is the C++/CLI compiler, it always assumes and that doesn't make programmers happy either. Add
static Form1()to see that it is allowed to mutate the jk2 value.– Hans Passant
4 hours ago