Just curious, is there a way to have a getter for a constant variable? I have a sort of internal version number to ensure that two versions of a library are still speaking the same language, but I'd like the programmer to be able to check what version they're using. Right now I use:
private const Int16 protocol_version = 1;
public Int16 ProtocolVersion => protocol_version;
But I'd prefer to do it with just the const if there's a way.
You could declare a property with only a get accessor (without even declaring the set accessor, not even private):
private const Int16 protocol_version = 1;
public Int16 ProtocolVersion => protocol_version;
This is not the same as defining a constant only: the constant would be resolved at compile time, so if you update the library without recompiling the dependent program, the program would still see the "old" value. Consider this example:
// The class library
using System;
namespace MyClassLibrary {
public class X {
public const Int16 protocol_version = 1;
public Int16 ProtocolVersion => protocol_version;
}
}
// The program
using System;
using MyClassLibrary;
class Program {
static void Main(string[] args) {
var x = new X();
Console.WriteLine($"Constant: {X.protocol_version0}");
Console.WriteLine($"Getter: {x.ProtocolVersion}");
}
}
Now, compile the first time and execute the program. You will see
Constant : 1
Getter : 1
Then, modify protocol_version to 2, and recompile the class library only, without recompiling the program, then put the new class library in the program folder and execute it. You will see:
Constant : 1
Getter : 2
The fact is that if it's just a constant, the value is replaced at compile time.
I think that what you are actually looking for is a static readonly variable: in that way, you will avoid the compile-time const replacement, and the variable will not be modifiable after initialization:
public static readonly Int16 protocol_version = 1;
You have to keep in mind the reason for the existance of getters/setters. It is to control access to an encapsulated variable, specifically to control how a variable is changed and who can change it. Since a const is set only once and remains read-only on runtime there is no reason to create a property for it. Setting the constant to public is completely acceptable since it is not a private variable that needs to be protected.
If you really... really want to make it a property then just define it as a readonly property, skip the setter entirely:
public Int16 ProtocolVersion => protocol_version;
But just so we are clear, I would say normally you would have public constants with the same coding style as properties:
public const Int16 ProtocolVersion = 1
Just do:
public const Int16 protocol_version = 1;
This will provide a public getter as a const cannot have a setter.
Constants cannot be reassigned, hence why they are called constant therefore just make protocol_version public
private const Int16 protocol_version = 1;
Related
Is there any difference between the following?
class C
{
// One:
public static readonly int ValueAsAMember = 42;
// Two:
public static int ValueAsAProperty { get { return 42; } }
}
I'm used to writing constants the first way (unless they're private/internal, in which case I use the const keyword), but I recently saw the second form.
Is there any advantage one way over the other in terms of readability, convention, performance, or anything else?
You have three choices:
public static readonly int Value = 42;
public static int Value { get { return 42; } }
public const int Value = 42;
Choose static readonly if the value will not change at runtime but might change in future versions of your code.
Choose a property if the value might change at runtime. Of course it won't change if you use the given code.
Choose const if the value is really a constant that will not even change in future versions (something like Math.PI or int.MinValue). And of course the use of const is limited by the type of the value.
The difference between const and static readonly is that the const value will be replaced on the call site. If you change the value of a const in a future version then all assemblies that rely on your class need to be recompiled using the new value.
The property requires a method call (calling a getter is a method call). So if the value is constant at runtime there is no need for that.
Yes, there is an advantage:
If the value gets changeable at any point in the future (e.g. in a future version of your code), in a way that it is, for example, time-dependent, you can support that in the read-only property without changing the public interface of your class.
If you have to replace a readonly field with a property, you will have to recompile any other assemblies that use your class.
There are two major differences:
The first is that fields cannot be on interfaces, whereas properties can. So if you want to use this in an interface, you have to use the property.
The second, more interesting, is that readonly fields CAN be modified, while the object is being constructed. Take the following code:
public class MyTestClass
{
public readonly int MyInt = 1;
public MyTestClass()
{
MyInt = 2;
}
}
If a caller does
new MyTestClass().MyInt
they will get 2. The same goes for static constructors for a static readonly field.
The way I see it, using the first way describes the intention of the value better - which is that it is immutable. When a person is looking at the class' interface, he will see that the value is read-only, and won't have to wonder whether it can be changed later (since in the second case he can't see the property's implementation).
An important thing to note about const declarations (I don't believe it's true for readonly) is that changing the field's value constitutes an API change, even if you're just changing the value from 42 to 41. The reason is that for consts, the value is determined during compile time, which means that if I compile a module that uses your constant, and you later change it, I will still be using the old value until I recompile my module with your new version.
readonly is nice to use on things that can only be changed in your constructor. Examples of this is typical services as interfaces when you are following the TDD pattern.
In your example const is best, it's a constant after all.
readonly
const
Cheers
I think the first line making something constant or rather readonly using readonly keyword.
and the second line is making use of a property to implement readonly. Both do the same but if you compare with the IL the property would add few extra lines of code to the dll.
The main advantage for me is with readonly you are allowed to declare it anywhere in your code. But, you will get a chance to set it only once. With the setter, you declare and set in one stroke.
Yes, there's a difference between the two.
A readonly field can only be set in the constructor.
A {get; private set;} can be set at anytime from within the class.
Example:
public class Car
{
public readonly string Name;
public string color {get; private set;}
public Car()
{
Name = "Car";
Color = "Red";
}
// will fail compilation
public void ModifyName()
{
Name = "Subaru"
}
// perfectly ok
public void ModifyColor()
{
Color = "Green"
}
}
A Property is just syntactic sugar around a field, a property without a setter is simply declared a readonly field so the compiler will allow you to set it at runtime in the constructor, because to the compiler you are referencing a readonly field. There is a larger discussion around what to use a field or property, which is not within the scope of the question. And yes its this syntactic sugar that you have to do the recompiling referenced by #SOreadytohelp. Just to be clear a property is a field with a get and set method created for it, C# will allow you to reference it like a field rather than doing an annoying call to the getter or setter everytime.
I'm learning C#,and now i'm trying to understand static members and constants.Which is the best way to declare a constant?
This way?
class Myclass
{
public const double G=9.8;
}
Or
class Myclass
{
private static double G{get;set;}
static MyClass()
{
G=9.8;
}
}
I've asked this question because,with the 2 ways i access the membre with the same code:
Console.WriteLine(Myclass.G);
constant:
Constant fields are defined at the time of declaration in the code
snippet, because once they are defined they can't be modified. By
default a constant is static, so you can't define them static from
your side.
It is also mandatory to assign a value to them at the time of
declaration otherwise it will give an error during compilation of the
program snippet. That's why it is also called a compile-time constant.
Explanation:
Consider ff. code:
void Sum(int j)
{
const int i = 9, k = 2;
const int A = i + k;
}
This will produce a result of 11, without showing any error since we already declared it at the initial point of declaration.
But how about:
void Sum(int j)
{
const int i = 9, k = 2;
//const int A = i + k;
Const int B = i + j;
}
This code snippet will take you toward a compile-time error, because there is no initialization, since it's evaluated at run time.
Points to Remember
Compile-time constant
Can't be declared static
Can't be modified or changed
Can be of any type of Access Modifier
Local scope
Needs to get initialized
Declared at the time of declaration
Static
The static keyword is used to declare a static member. If we are
declare a class as a static class then in this case all the class
members must be static too. The static keyword can be used effectively
with classes, fields, operators, events, methods and so on
effectively.
Consider ff. code:
class ReadOnly
{
static int i = 11;
public static void disp()
{
Console.WriteLine(i);
}
}
Explanation:
This code will show no error and produce a result (11), since we declared its value to be static at the time of declaration. So we can access it depending on our use in the program.
But how about this:
class ReadOnly
{
int i = 9;
public static void disp()
{
Console.WriteLine(i);
}
}
This snippet above will show an error, because we didn't declare a value for the static and we are trying to access it within a method. We can't do that.
Points to Remember:
Can't be used with indexers
Works with constructors too
By default it is private
Can be parameterized or public too
If its applied to a class then all the class members need to be static
You can read more about above explanation here: constant vs readonly vs static
Additional note for static methods.
Consider ff. code:
public class SomeClass {
public string SomeMethod() {
return "Hello, World.";
}
}
When you want to Access SomeMethod of SomeClass, you need to instantiate SomeClass first:
var some = new SomeClass();
string result = some.SomeClass(); //this will set result as "Hello, World."
Compared to a static method:
public class SomeClass {
public static string SomeMethod() {
return "Hello, World.";
}
}
When accessing SomeMethod, you don't need to instantiate SomeClass. You can access it directly by:
string result = SomeClass.SomeMethod(); //this will give "Hello, World."
Which is the best way to declare a constant?
Its not the best, its the only way: const double G = 9.8;.
Or (...) static double G { get; set; }
Thats not a constant! Constant means constant: 1 is a constant, 'c'is a constant, PI is a constant... they represent values that don't change, ever!. Your second implementation of G can change, therefore its not a constant.
Also, its important you notice that constants are known at compile time, there is no evaluation needed at runtime.
This is the reason why any reference type const (expect string which has specific compiler support through string literals) can only be initialized to null, any other option would need to be evaluated at runtime.
Its also the reason why only a finite set of value types can be declared as const too. All of them are existing types in the framework and.. surprise, surprise, they all have compiler literal constant support: 1, 'c', 9.8 or 0.25M but not 01/01/2017 (how else would the compiler know the values before runtime?).
Another interesting question you didn't make is: what about static readonly?
You can think of static readonly as "the poor man's" const. Its often used to circumvent the limitations const offers concerning what types and initializing values are allowed.
It is almost the same as a constant, but there are a few important and decisive differences:
It can change; although it is readonly, you can change it's value inside the static constructor of the declaring type. const can never change after initialized.
It is evaluated at runtime, not compile time as a true const.
Any type can be declared as a static readonly and initialized to any valid value as you would do with any regular field.
As a nittpicking side note, you shouldn't make G a constant ;). It changes, and quite a bit. G in Ecuador is different from G in the North Pole.
const variables are assigned values at time of definition.
They are available at compile time. You can even use a compile time evaluate-able expression at compile time. But once a value has been assigned to a const variable, it cannot be changed at any other time.
Using static field means the value will remain same for every user of the application, but this value can be changed by code in any of the classes, and it will change for every user of the application.
Do not use static for constants, use const only. const are by default static, and you cannot use static keyword with it.
Check this
void Main()
{
// You will not be able to change value for const variable.
Console.WriteLine(Myclass.G);
// You will be able to change value for static variable,
// and this change will impact all users of the application.
// For every user, this field will store value of 10 now.
// That will not be required or desired code behavior.
Myclass1.G = 10;
Console.WriteLine(Myclass1.G);
}
// Normal class with const field
class Myclass
{
public const double G=9.8;
}
//static class with static constructor
static class Myclass1
{
public static double G{get;set;}
static Myclass1()
{
G=9.8;
}
}
Read More
Here you are talking about two different things, and this is their definition from MSDN:
1- static modifier: To declare a static member, which belongs to the type itself rather than to a specific object. The static modifier can be used with classes, fields, methods, properties, operators, events, and constructors, but it cannot be used with indexers, finalizers, or types other than classes.
2- const keyword: To declare a constant field or a constant local. Constant fields and locals aren't variables and may not be modified. Constants can be numbers, Boolean values, strings, or a null reference. Don’t create a constant to represent information that you expect to change at any time.
So a static member is defined for a Class (for all its instances, and that's why you can access it directly from the name of the Class) but can be modified. a const field of class can not be modified.
I have a c# program and I have some constant variables that I want to be accessible throughout the program. I won't need to change them at any point.
I have tried a static class and that worked well. I declared a 'static class' and had my variables inside as 'public static'.
The problem came when I wanted to use these unchanging variables in a case statement. Since this only accepts consts, it didn't work out too well.
The question is this: if I have a static class which does not have static variables within it, will this work just as well? This is going from public static to public const.
Thanks for your help.
Yes, consts by default are static.
It depends. Const can't be variables, they must be literals. If you're trying to assign a variable to the const such as a class you made then you have to keep it as static readonly. If you mean to assign a literal such as a number or a string then const is just fine.
A few examples:
public const int Number = 1; // this works; 1 is a literal
public const int Number = SomeClass.SomeProperty; // this does not work
public const int Number = SomeClass.SomeConst; // this works
public const SomeClass Var = new SomeClass(); // does not work
public const string Var = "test"; // this works as "test" is a literal.
If you are not using literals youre better of doing:
public static readonly SomeClass Var = new SomeClass ();
If you are using numeric literals another option is the enum which is basically a static class with some added features.
public enum MyConstants
{
VarOne, // defaults to 0
VarTwo, // defaults to next number (1)
VarThree // defaults to next number (2)
}
Is there any alternative present for Static Field in C# as static field never garbage collected?
If I want to declaure the number of strings, constants which I want to use throughout the program, I am finding a way for that.
You can use a const but it has to be a value.
public class Foo
{
public const string Bar = "Bar";
}
See https://msdn.microsoft.com/en-us/library/e6w8fe1b.aspx
As an addition to Richard Schneiders answer, sometimes you can't use const (the compiler should know the const value at the compiling time), but want to provide constant like behaviour. In that case readonly is the choice:
public class Foo {
// Settings should be read and then preserved intact
public static readonly String Settings = File.ReadAllText(#"C:\MySettings.txt");
...
}
You can Use Const for this.
Const is a reserved word. It allows us to specify that a value is invariant and must not be modified after compile-time. Const values, like const strings, help us simplify and optimize programs.
Eg:
public static class Constants
{
public const string Name = "abc";
}
https://msdn.microsoft.com/en-us/library/acdd6hb7.aspx
Is there any difference between the following?
class C
{
// One:
public static readonly int ValueAsAMember = 42;
// Two:
public static int ValueAsAProperty { get { return 42; } }
}
I'm used to writing constants the first way (unless they're private/internal, in which case I use the const keyword), but I recently saw the second form.
Is there any advantage one way over the other in terms of readability, convention, performance, or anything else?
You have three choices:
public static readonly int Value = 42;
public static int Value { get { return 42; } }
public const int Value = 42;
Choose static readonly if the value will not change at runtime but might change in future versions of your code.
Choose a property if the value might change at runtime. Of course it won't change if you use the given code.
Choose const if the value is really a constant that will not even change in future versions (something like Math.PI or int.MinValue). And of course the use of const is limited by the type of the value.
The difference between const and static readonly is that the const value will be replaced on the call site. If you change the value of a const in a future version then all assemblies that rely on your class need to be recompiled using the new value.
The property requires a method call (calling a getter is a method call). So if the value is constant at runtime there is no need for that.
Yes, there is an advantage:
If the value gets changeable at any point in the future (e.g. in a future version of your code), in a way that it is, for example, time-dependent, you can support that in the read-only property without changing the public interface of your class.
If you have to replace a readonly field with a property, you will have to recompile any other assemblies that use your class.
There are two major differences:
The first is that fields cannot be on interfaces, whereas properties can. So if you want to use this in an interface, you have to use the property.
The second, more interesting, is that readonly fields CAN be modified, while the object is being constructed. Take the following code:
public class MyTestClass
{
public readonly int MyInt = 1;
public MyTestClass()
{
MyInt = 2;
}
}
If a caller does
new MyTestClass().MyInt
they will get 2. The same goes for static constructors for a static readonly field.
The way I see it, using the first way describes the intention of the value better - which is that it is immutable. When a person is looking at the class' interface, he will see that the value is read-only, and won't have to wonder whether it can be changed later (since in the second case he can't see the property's implementation).
An important thing to note about const declarations (I don't believe it's true for readonly) is that changing the field's value constitutes an API change, even if you're just changing the value from 42 to 41. The reason is that for consts, the value is determined during compile time, which means that if I compile a module that uses your constant, and you later change it, I will still be using the old value until I recompile my module with your new version.
readonly is nice to use on things that can only be changed in your constructor. Examples of this is typical services as interfaces when you are following the TDD pattern.
In your example const is best, it's a constant after all.
readonly
const
Cheers
I think the first line making something constant or rather readonly using readonly keyword.
and the second line is making use of a property to implement readonly. Both do the same but if you compare with the IL the property would add few extra lines of code to the dll.
The main advantage for me is with readonly you are allowed to declare it anywhere in your code. But, you will get a chance to set it only once. With the setter, you declare and set in one stroke.
Yes, there's a difference between the two.
A readonly field can only be set in the constructor.
A {get; private set;} can be set at anytime from within the class.
Example:
public class Car
{
public readonly string Name;
public string color {get; private set;}
public Car()
{
Name = "Car";
Color = "Red";
}
// will fail compilation
public void ModifyName()
{
Name = "Subaru"
}
// perfectly ok
public void ModifyColor()
{
Color = "Green"
}
}
A Property is just syntactic sugar around a field, a property without a setter is simply declared a readonly field so the compiler will allow you to set it at runtime in the constructor, because to the compiler you are referencing a readonly field. There is a larger discussion around what to use a field or property, which is not within the scope of the question. And yes its this syntactic sugar that you have to do the recompiling referenced by #SOreadytohelp. Just to be clear a property is a field with a get and set method created for it, C# will allow you to reference it like a field rather than doing an annoying call to the getter or setter everytime.