What I want to do is allow the public incrementation of an integer value within my class, but not allow it to be publicly set explicitly.
I know that I can create a function like this:
void IncrementMyProperty()
but I'd like to allow the user to just do this:
MyClass.Property++;
without allowing this:
MyClass.Property = <SomeInt>;
It's merely for convenience. I'm just wondering if there is any way to do it.
Here's an example:
class MyClass
{
private int _count;
public int Count
{
get { return _count; }
private set { _count = value; }
}
public void AddOne()
{
_count++;
}
}
class Program
{
static void Main()
{
MyClass example;
for (int i = 0; i < 10; i++)
example.Count++;
}
}
Obviously this won't compile. It's just to show what I'd like to do.
Well, it's possible, but the solution is pretty ugly.
You can create a type that overloads the ++ operator, and make a property of that type where the setter does nothing. That will allow you to use the ++ operator on the property, but it's not possible to actually set the property using the property setter:
class MyValue {
public int Value { get; private set; }
public MyValue(int value) {
Value = value;
}
public static MyValue operator ++(MyValue v) {
v.Value++;
return v;
}
}
class MyClass {
private MyValue _count = new MyValue(0);
public MyValue Count {
get { return _count; }
set { }
}
}
Usage:
MyClass c = new MyClass();
c.Count++;
Console.WriteLine(c.Count.Value); // outputs 1
So... using the ++ operator in that way is not a good solution. Normally you don't have a setter that does nothing, that will only be confusing. Having a method that increases the counter is not as short as writing ++, but it won't be confusing as long as you name it so that it's clear what it does.
There's no way. MyClass.MyProperty++ literally translates to MyClass.MyProperty = MyClass.MyProperty + 1, which uses a "setter" and if you allow a "setter" accessor then you would allow, for example, MyClass.MyProperty = <any value>;
not if you increment the int property. but you could write example++ and overload the ++ operator for your class to increment Count, while removing its setter.
Related
I understand how Auto-Implemented Properties work and how they are supposed to help. I was wondering if I could still use it somehow in a more advanced way.
Imagine I have this:
public int SomeProperty { get; set; }
Which is basically another way of writing the code below (but using Automatic Properties).
private int _someField;
public int SomeProperty
{
get { return _someField;}
set { _someField = value;}
}
What I want to do is write:
private int _someField;
public int SomeProperty
{
get { return _someField;}
set { FunctionA(); _someField = value;}
}
But using the advantages of the Auto-Implemented Properties. Is that possible?
I tried something like this:
public int SomeProperty { get; set{FunctionA();} }
But it doesn't work. Thank you everybody for the help, I know it's silly but I am curious about it.
No, it is not allowed. See the language spec:
https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/language-specification/classes#properties
An automatically implemented property (or auto-property for short), is a non-abstract non-extern property with semicolon-only accessor bodies.
I didn't find free tool, but PostSharp handles this. It has trial period and some free-to-use options. Anyway take a look at method decoration and AOP frameworks.
using System;
using PostSharp.Aspects;
namespace ConsoleApp
{
class Program
{
static void Main(string[] args)
{
var someClass = new SomeClass();
Console.WriteLine($"{nameof(someClass.Value)} = {someClass.Value}");
someClass.Value = 42;
Console.WriteLine($"{nameof(someClass.Value)} = {someClass.Value}");
}
}
class SomeClass
{
public int Value { get; [Decorate] set; }
private void SomeFunction()
{
Console.WriteLine("SomeFunction called");
}
[Serializable, AttributeUsage(AttributeTargets.Method)]
public class DecorateAttribute : MethodInterceptionAspect
{
public override void OnInvoke(MethodInterceptionArgs args)
{
var target = (SomeClass)args.Instance;
target.SomeFunction();
args.Proceed(); // performs the method it applied to
}
}
}
}
Output:
Value = 0
SomeFunction called
Value = 42
I am learning about writing constructors and properties in c# and was asked to write a console app and class to operate a beverage machine. I wrote part of the class code but ran into an issue. One of the many blocks of code asks for a constructor method that starts the SodaCanCount at 5 bottles and sets the CustBalance field to zero. I don't know what this constructor should look like. I am specifically talking about the private sodaVandorClass(), right under the two private fields.
I wrote what I could so far and I have no errors however the SodaVendorClass does not look right.
namespace VendorClass
{
public class SodaVendorClass
{
// members
// fields
//Customer balance is $0 until the customer inserts a dollar
//All customer entries are one dollar increments and a soda costs one dollar.
private int CustBalance = 0;
//a machine holds 10 cans of soda
private int SodaCanCount = 5;
//A soda costs 1 dollar
//private int sodaCost = 1;
public int _SodaCanCount
{
get
{
return SodaCanCount;
}
}
public int _CustBalance
{
get
{
return CustBalance;
}
}
public int BuySoda(int pCustBalance, int SodaCanCount)
{
return SodaCanCount;
}
public void AcceptCash(int CustBalance)
{
CustBalance++;
}
public int GiveRefund(int pCustBalance)
{
return CustBalance;
}
}
I only want to see an example of a constructor that sets default values for my private class fields. Any help will be appreciated.
You can define a public constructor like below but probably you don't need one if you enable your properties to set values too
public SodaVendorClass()
{
this.CustBalance = 0;
this.SodaCanCount = 0;
}
You can make your properties writable too. Notice below are auto properties and in such case you don't need those private backing fields explicitly.
public int SodaCanCount
{
get; set;
}
public int CustBalance
{
get; set;
}
You can instantiate your type saying (using Object Initializer construct)
SodaVendorClass sc = new SodaVendorClass
{
SodaCanCount = 10,
CustBalance = 500,
};
A constructor for this class could look like this:
public SodaVendorClass () {
}
That would be an empty constructor that does nothing.
To set the two values you want, you can add some paramters:
public SodaVendorClass (int customerBalance, int sodaCount) {
this.CustBalance = customerBalance;
this.SodaCanCount = sodaCount;
}
To create an instance of this class with 5 soda cans and a customer balance of 0, you would call the constructor in the code like this:
var vendor = new SodaVendorClass(0, 5);
namespace VendorClass
{
public class SodaVendorClass
{
private int CustBalance;
private int SodaCanCount;
//...
public SodaVendorClass() // default constuctor
{
CustBalance = 0;
SodaCanCount = 5;
}
//...
}
}
Default constructor is called when you are creating object like this:
SodaVendorClass obj = new SodaVendorClass();
So obj._SodaCanCount is 5 and obj._CustBalance is 0
Also you can define constructor with parameters.
public SodaVendorClass(int balance, int count)
{
CustBalance = balance;
SodaCanCount = count;
}
and create call this constructor.
SodaVendorClass obj = new SodaVendorClass(0, 5);
A constructor is being used while creating a object like "Class obj=new Calss()". If you don define a constructor in your class a default constructor will be provided implicitly.User defined Constructor usually used for initializing value for class properties. Unlike function constructor does not have any return type at all not even void. All the answers are good.
public class SodaVendorClass{
private int CustBalance = 0;
//a machine holds 10 cans of soda
private int SodaCanCount = 5;
//A soda costs 1 dollar
//private int sodaCost = 1;
public int _SodaCanCount
{
get
{
return SodaCanCount;
}
}
public int _CustBalance
{
get
{
return CustBalance;
}
}
public SodaVendorClass(int cancount, int sodacost){
SodaCanCount=cancount;
sodaCost=sodacost;
}
}
//creating a object of Sodavendorclass
Sodavendorclass obj=new Sodavendorclass(0,0); //Provided value for class property
Notice that at the time of object creation, provided for Property. This is one of the way you can use constructor.
In Encapsulation get is readonly where set is write only
Why my output is 11110 when not using special member function?
code:
class practice_4
{
static void Main(string[] args)
{
example ABC = new example();
// ABC.Roll_ = 11;
Console.WriteLine(ABC.Roll_ );
Console.ReadLine();
}
}
class example
{
private int roll = 11110;
public int Roll_
{
get
{
return roll ;
}
//set{
// if (value > 10)
// { roll = value; }
// else
// { Console.WriteLine("error"); }
//}
}
//public example()
//{
// roll = 110;
//}
}
Output :
11110
but when I use special member function : public example()
class practice_4
{
static void Main(string[] args)
{
example ABC = new example();
Console.WriteLine(ABC.Roll_ );
Console.ReadLine();
}
}
class example
{
private int roll = 11110;
public int Roll_
{
get
{
return roll ;
}
}
public example()
{
roll = 110;
}
}
so It display Output:
110
and discard 11110
To Answer your question "Why my output is 11110 when not using special member function?"
The special member function in your class is the Constructor of your class, which means this is the special function that initializes/constructs your object from your class definition, rule to remember here is, constructors are called after your private variables statements and also when the constructor is finished the construction is finished, which means your class's internal state(variables) are now assigned(among other things).
However if you initialize the private variables like you are in private int roll = 11110; line, this line executes before the constructor is called. but as you are overwriting the value of roll in constructor, the value of your private variable gets overwritten.
In the example class you are calling the roll variable instead of the Roll_ property. If you were to try to set Roll_ instead you would get a compile time error saying something along the lines of you cannot modify a read-only property. The purpose of encapsulation is to prevent the outside world from directly modifying the value, it's not in place to prevent the class from modifying the value.
I want to know that when you create an Automatic property
and invoke the set in the main() method for a random value , where is that value being stored ?as in this example :
class Program
{
static void Main(string[] args)
{
Example W = new Example();
W.Num = 10;
Console.WriteLine("{0}", W.Num);
Console.WriteLine("{0}", W.getNum());
}
}
class Example
{
private int num;
public int Num { get; set; }
public int getNum() { return num; }
}
why is the output :
100
Because you are returning num, not Num. And num was not initialized, so this value is 0.
Auto-implemented properties makes code cleaner when no additional logic is required for the getter or setter. The compiler actually generates a backing field for the auto-implemented property, but this backing field is not visible from your code.
In your example there is no connection between the num field and the Num property, so there no reason why the num should change.
This is nothing abnormal here.
When you call
Example W = new Example();
then initially num = 0 and Num = 0;
you assigned Num, not num.
num in your Example class is redundant.
If you wrote this before automatic property initialisers were added to c#, it would look like this:
private int num;
public int Num
{
get{ return num;}
set{ num = value;}
}
Writing public public int Num { get; set; } is essentially the same thing behind the scenes. There is no need to implement getNum() (like Java), since this is equivalent to int a = w.Num;.
if use new keyword , you created new instance your class And all object recreated.
For Example ;
class Program
{
static void Main(string[] args)
{
Example W = new Example();
W.Num = 10;
Example W1 = new Example();
Console.WriteLine("{0}", W.Num); //10
Console.WriteLine("{0}", W1.Num); //0
}
}
this is only information your answer ; you returning different variable. you not set them.
[Edit: It looks like the original question involved a double and not an integer. So I think this question stands if we change the integer to a double.]
I have rare issue with reading integer properties from a class used in multiple threads that sometimes returns a zero value. The values are not changed after initialization.
This question addresses that. The consensus is that even though I'm accessing an integer I need to synchronize the properties. (Some of the original answers have been deleted). I haven't chosen an answer there because I have not resolved my issue yet.
So I’ve done some research on this and I’m not sure which of .Net 4’s locking mechanisms to use or if the locks should be outside the class itself.
This is what I thought about using:
public class ConfigInfo
{
private readonly object TimerIntervalLocker = new object();
private int _TimerInterval;
public int TimerInterval
{
get
{
lock (TimerIntervalLocker) {
return _TimerInterval;
}
}
}
private int _Factor1;
public int Factor1
{
set
{
lock (TimerIntervalLocker) {
_Factor1 = value;
_TimerInterval = _Factor1 * _Factor2;
}
}
get
{
lock (TimerIntervalLocker) {
return _Factor1;
}
}
}
private int _Factor2;
public int Factor2
{
set
{
lock (TimerIntervalLocker) {
_Factor2 = value;
_TimerInterval = _Factor1 * _Factor2;
}
}
get
{
lock (TimerIntervalLocker) {
return _Factor2;
}
}
}
}
But I’ve read that this is horribly slow.
Another alternative is to lock the instance of ConfigData on the user side but that seems to be a lot of work. Another alternative I’ve seen is Monitor.Enter and Monitor.Exit but I think Lock is the same thing with less syntax.
So what is a best practice for making a class's properties thread
safe?
a. Using lock can be slow since it uses operating system resources, if the properties' complexity is low, then spin lock (or interlocked.compareexchange) will be faster.
b. You have to make sure that a thread won't enter a lock and via a call from one property to another get locked out. - If this can happen (non currently an issue in your code), you'll need to make the lock thread or task sensitive.
Edit:
If the object is supposed to be set during initialization and never changed, make it immutable (like .NET strings are). Remove all the public setters and provide a constructor with parameters for defining the initial state and perhaps additional methods/operators for creating a new instance with a modified state (e.g. var newString = "Old string" + " was modified.";).
If the values never change, it would be easier to just make a copy of that instance and pass each thread an instance of it's own. No locking required at all.
I think you should rewrite your ConfigInfo class to look like this; then you can't get overflow or threading problems:
public sealed class ConfigInfo
{
public ConfigInfo(int factor1, int factor2)
{
if (factor1 <= 0)
throw new ArgumentOutOfRangeException("factor1");
if (factor2 <= 0)
throw new ArgumentOutOfRangeException("factor2");
_factor1 = factor1;
_factor2 = factor2;
checked
{
_timerInterval = _factor1*_factor2;
}
}
public int TimerInterval
{
get
{
return _timerInterval;
}
}
public int Factor1
{
get
{
return _factor1;
}
}
public int Factor2
{
get
{
return _factor2;
}
}
private readonly int _factor1;
private readonly int _factor2;
private readonly int _timerInterval;
}
Note that I'm using checked to detect overflow problems.
Otherwise some values will give incorrect results.
For example, 57344 * 524288 will give zero in unchecked integer arithmetic (and there's very many other pairs of values that will give zero, and even more that will give a negative result or a positive value that "seems" correct).
It is best, as mentioned in the comments, to make the properties readonly. I thought about the following possibility:
public class ConfigInfo
{
private class IntervalHolder
{
public static readonly IntervalHolder Empty = new IntervalHolder();
private readonly int _factor1;
private readonly int _factor2;
private readonly int _interval;
private IntervalHolder()
{
}
private IntervalHolder(int factor1, int factor2)
{
_factor1 = factor1;
_factor2 = factor2;
_interval = _factor1*_factor2;
}
public IntervalHolder WithFactor1(int factor1)
{
return new IntervalHolder(factor1, _factor2);
}
public IntervalHolder WithFactor2(int factor2)
{
return new IntervalHolder(_factor1, factor2);
}
public int Factor1
{
get { return _factor1; }
}
public int Factor2
{
get { return _factor2; }
}
public int Interval
{
get { return _interval; }
}
public override bool Equals(object obj)
{
var otherHolder = obj as IntervalHolder;
return
otherHolder != null &&
otherHolder._factor1 == _factor1 &&
otherHolder._factor2 == _factor2;
}
}
private IntervalHolder _intervalHolder = IntervalHolder.Empty;
public int TimerInterval
{
get { return _intervalHolder.Interval; }
}
private void UpdateHolder(Func<IntervalHolder, IntervalHolder> update)
{
IntervalHolder oldValue, newValue;
do
{
oldValue = _intervalHolder;
newValue = update(oldValue);
} while (!oldValue.Equals(Interlocked.CompareExchange(ref _intervalHolder, newValue, oldValue)));
}
public int Factor1
{
set { UpdateHolder(holder => holder.WithFactor1(value)); }
get { return _intervalHolder.Factor1; }
}
public int Factor2
{
set { UpdateHolder(holder => holder.WithFactor2(value)); }
get { return _intervalHolder.Factor2; }
}
}
This way, your TimerInterval value is always in sync with its factors. The only problem is when some thread reads one of the properties while another writes them from outside the ConfigInfo. The first one could get wrong value and I don't see any way to solve this without introducing a single lock root. The question is whether read operations are critical.