# Amusing C\#

To assess the quality of PVS\-Studio C\# diagnostics, we test it on a large number of software projects\. Since projects are written by different programmers from different teams and companies, we have to deal with different coding styles, shorthand notations, and simply different language features\. In this article, I will give an overview of some of the features offered by the wonderful C\# language, as well as the issues that one may run into when writing in this language\. 

![0403_Amusing_CSharp/image1.png](https://import.viva64.com/docx/blog/0403_Amusing_CSharp/image1.png)

A little note\. 

This article was mostly written for the sake of curiosity and describes those things that were of interest to me personally\.

## Properties and how they can be used

As we all know, a property is a pair of functions \- accessor and mutator \- designed for writing or reading the value of a field\. At least, things used to be that way before the release of C\# version 3\.0\. In its traditional form, a property used to look like this:

```cpp
class A
{
  int index;
  public int Index
  {
    get { return index; }
    set { index = value; }
  }
}
```

Years went by, and both the language standards and properties have acquired a number of new mechanisms\.

So, here we go\. The C\# 3\.0 standard brought us the well\-known feature that allowed you to omit the field; that is, to declare a property in the following way:

```cpp
class A
{
  public int Index { get; set; }
}
```

The idea was pushed even further in C\# 6\.0 by allowing programmers to omit "set" as well:

```cpp
class A
{
  public int Index { get; }
}
```

It was possible to use this style before C\# 6\.0 too, but you could not assign anything to a variable declared in such a way\. Now it has in fact become an equivalent to _readonly_ fields, i\.e\. the values of such properties can be assigned only in the constructor\. 

Properties and fields can be initialized in different ways\. For example, like this:

```cpp
class A
{
  public List<int> Numbers { get; } = new List<int>(); 
}
```

Or like this:

```cpp
class A
{
  public List<int> Numbers = new List<int>();
}
```

One more version:

```cpp
class A
{
  public List<int> Numbers => new List<int>();
}
```

In the last case, though, you will be unpleasantly surprised\. You see, what we have actually created there is the following property:

```cpp
class A
{
  public List<int> Numbers { get { return new List<int>(); } }
}
```

That is, an attempt to fill _Numbers_ with values will inevitably fail; you'll be getting a new list every time\. 

```cpp
A a = new A();
a.Numbers.Add(10);
a.Numbers.Add(20);
a.Numbers.Add(30);
```

So be careful when using shorthand notations, as it may result in long bug\-hunting sometimes\.

These are not all the interesting features of properties\. As I have already said, a property is a pair of functions, and in C\# nothing prevents you from changing the parameters of functions\.

For example, the following code compiles successfully and even executes:

```cpp
class A
{
  int index;
  public int Index
  {
    get { return index; }
    set { 
      value = 20; 
      index = value; }
  }
}
static void Main(string[] args)
{
  A a = new A();
  a.Index = 10;
  Console.WriteLine(a.Index);
}
```

However, the program will always output the number "20", but never "10"\.

You may wonder why one would need to assign the value 20 to _value_? Well, it appears to make sense\. To explain this point, however, we'll have to set our discussion of properties aside for a while and talk about the _@_ prefix\. This prefix allows you to declare variables that resemble keywords in spelling, for example  _@this_, _@operator_ and so on\. At the same time, you are not prohibited from inserting this character wherever you please, for example:

```cpp
class A
{
  public int index;
  public void CopyIndex(A @this)
  {
    this.@index = @this.index;
  }
}
static void Main(string[] args)
{
  A a = new A();
  @a.@index = 10;
  a.@CopyIndex(new A() { @index = 20 });
  Console.WriteLine(a.index);
}
```

The output, as everywhere in this article, is the number "20", but never "10"\.

The _@_ prefix is actually required in one place only: when writing parameter name _@this_ in the _CopyIndex_ function\. When used elsewhere, it's just redundant code, which also lacks clarity\.

Now that we know all that, let's get back to properties and take a look at the following class:

```cpp
class A
{
  int value;
  public int Value
  {
    get { return @value; }
    set { @value = value; }
  }
  public A()
  {
    value = 5;
  }
}
```

You may think that the _value _field of class _A _will change in the _Value_ property, but it won't, and the following code will output 5, not 10\.

```cpp
static void Main(string[] args)
{
  A a = new A();
  a.Value = 10;
  Console.WriteLine(a.Value);
}
```

This behavior is the result of the mismatch of _@value in get and @value in set\. In get, @value will be nothing more but a field of an A class\. At the same time, in set, the @valueis a parameter of the set function\. Thus_ _we_ _just_ _write_ _value_ _in_ _itself_ _and_ _do_ _not_ _touch_ _value_ _filed_ _in_ _the_ _A_ _class\._ 

## Collection initialization

Let's first recall different methods of how arrays can be initialized:

```cpp
string[] test1 = new string[] { "1", "2", "3" };
string[] test2 = new[] { "1", "2", "3" };
string[] test3 = { "1", "2", "3" };
string[,] test4 = { { "11", "12" }, 
                    { "21", "22" }, 
                    { "31", "32" } };
```

Lists are simpler and there is only one variant of initialization:

```cpp
List<string> test2 = new List<string>(){ "1", "2", "3" };
```

Now, what about dictionaries?: 

```cpp
Dictionary<string, int> test = 
  new Dictionary<string, int>() { { "a-a", 1 }, 
                                  { "b-b", 2 }, 
                                  { "c-c", 3 } };
```

This one I saw for the first time, so this section is written mainly because of it:

```cpp
Dictionary<string, int> test = 
  new Dictionary<string, int>() { 
    ["a-a"] = 1,
    ["b-b"] = 2,
    ["c-c"] = 3
  };
```



## A few words about LINQ queries

LINQ queries are in themselves a convenient feature: you make a sequence of necessary samples and get the required information at the output\. Let's first discuss a couple of nice tricks that may not occur to you until you see them\. Let's start with a basic example:

```cpp
void Foo(List<int> numbers1, List<int> numbers2) {
  var selection1 = numbers1.Where(index => index > 10);
  var selection2 = numbers2.Where(index => index > 10);
}
```

As you can easily see, the code above contains several identical checks, so it would be better to enclose them in a separate "function":

```cpp
void Foo(List<int> numbers1, List<int> numbers2) {
  Func<int, bool> whereFunc = index => index > 10;
  var selection1 = numbers1.Where(index => whereFunc(index));
  var selection2 = numbers2.Where(index => whereFunc(index));
}
```

It looks better now; if functions are large, it's better still\. The _whereFunc_ call, however, looks somewhat untidy\. Well, it's not a problem either:

```cpp
void Foo(List<int> numbers1, List<int> numbers2) {
  Func<int, bool> whereFunc = index => index > 10;
  var selection1 = numbers1.Where(whereFunc);
  var selection2 = numbers2.Where(whereFunc);
}
```

Now the code does look compact and neat\. 

Now let's talk about the specifics of LINQ\-query execution\. For example, the following code line won't trigger immediate sampling of data from the _numbers1_ collection\.

```cpp
IEnumerable<int> selection = numbers1.Where(whereFunc);
```

Sampling will start only after the sequence has been converted into the _List<int\>_ collection:

```cpp
List<int> listNumbers = selection.ToList();
```

This nuance may cause a captured variable to be used after its value has changed\. Here's a simple example\. Suppose we need function _Foo_ to return only those elements of the "\{ 1, 2, 3, 4, 5 \}" array whose numerical values are less than the current element's index\. In other words, we need it to output the following:

```cpp
0 :
1 :
2 : 1
3 : 1, 2
4 : 1, 2, 3
```

Our function will have the following signature:

```cpp
static Dictionary<int, IEnumerable<int>> Foo(int[] numbers)
{ ....  }
```

And this is how we will call  it:

```cpp
foreach (KeyValuePair<int, IEnumerable<int>> subArray in 
           Foo(new[] { 1, 2, 3, 4, 5 }))
Console.WriteLine(string.Format("{0} : {1}", 
                  subArray.Key, 
                  string.Join(", ", subArray.Value)));
```



It doesn't seem to be difficult\. Now let's write the LINGQ\-based implementation itself\. This is what it will look like:

```cpp
static Dictionary<int, IEnumerable<int>> Foo(int[] numbers)
{
  var result = new Dictionary<int, IEnumerable<int>>();
  for (int i = 0; i < numbers.Length; i++)
    result[i] = numbers.Where(index => index < i);
  return result;
}
```

Very easy, isn't it? We just "make" samples from the _numbers_ array one by one\.

However, what the program will output in the console is the following:

```cpp
0 : 1, 2, 3, 4
1 : 1, 2, 3, 4
2 : 1, 2, 3, 4
3 : 1, 2, 3, 4
4 : 1, 2, 3, 4
```

The problem with our code has to do with the closure in the lambda expression _index \=\> index < i_\. The _i_ variable was captured, but because the lambda expression _index \=\> index < i_ was not called until the _string\.Join\(", ", subArray\.Value\)_ function was requested to return, the value that the variable referred to was not the same as when the LINQ query had been formed\. When retrieving data from the sample, the _i_ variable was referring to 5, which resulted in incorrect output\.

## Undocumented kludges in C\#

The C\+\+ language is famous for its hacks, workarounds, and other kludges \- the series of _XXX\_cast_ functions alone counts for a lot\. It is commonly believed that C\# doesn't have any such things\. Well, it's not quite true\.\.\. 

Here are a few keywords, for a start:

* \_\_makeref
* \_\_reftype
* \_\_refvalue

These words are unknown to IntelliSense, nor will you find any official MSDN entries on them\.

So what are these wonder words?

_\_\_makeref_ takes an object and returns some "reference" to it as an object of type _TypedReference_\. And as for the words _\_\_reftype_ and _\_\_refvalue_, they are used, respectively, to find out the type and the value of the object referred to by this "reference"\.

Consider the following example:

```cpp
struct A { public int Index { get; set; } }
static void Main(string[] args)
{
  A a = new A();
  a.Index = 10;
  TypedReference reference = __makeref(a);
  Type typeRef = __reftype(reference);
  Console.WriteLine(typeRef); //=> ConsoleApplication23.Program+A
  A valueRef = __refvalue(reference, A);
  Console.WriteLine(valueRef.Index); //=> 10
}
```

Well, we could do this "stunt" using more common syntax:

```cpp
static void Main(string[] args)
{
  A a = new A();
  a.Index = 10;
  dynamic dynam = a;
  Console.WriteLine(dynam.GetType());
  A valuDynam = (A)dynam;
  Console.WriteLine(valuDynam.Index);
}
```

The _dynamic_ keyword allows us to both use fewer lines and avoid questions like "What's that?" and "How does it work?" that programmers not familiar with those words may ask\. That's fine, but here's a somewhat different scenario where _dynamic_ doesn't look that great compared to _TypedReference_\.

```cpp
static void Main(string[] args)
{
  TypedReference reference = __makeref(a);
  SetVal(reference);
  Console.WriteLine(__refvalue(reference, A).Index);
}
static void SetVal(TypedReference reference)
{
  __refvalue(reference, A) = new A() { Index = 20 };
}
```

The result of executing this code is outputting the number "20" in the console\. Sure, we could pass _dynamic_ into the function using _ref_, and it would work just as well\. 

```cpp
static void Main(string[] args)
{
  dynamic dynam = a;
  SetVal(ref dynam);
  Console.WriteLine(((A)dynam).Index);
}
static void SetVal(ref dynamic dynam)
{
  dynam = new A() { Index = 20 };
}
```

Nevertheless, I find the version with _TypedReference_ better, especially when you need to pass the information on and on through other functions\.

There is one more wonder word, _\_\_arglist_, which allows you to declare a variadic function whose parameters can also be of any type\.

```cpp
static void Main(string[] args)
{
  Foo(__arglist(1, 2.0, "3", new A[0]));
}
public static void Foo(__arglist)
{
  ArgIterator iterator = new ArgIterator(__arglist);
  while (iterator.GetRemainingCount() > 0)
  {
    TypedReference typedReference = 
      iterator.GetNextArg();
    Console.WriteLine("{0} / {1}",
      TypedReference.ToObject(typedReference),
      TypedReference.GetTargetType(typedReference));
   }
}
```

It is strange that the _foreach_ statement_ _can't be used as an out\-of\-the\-box solution to iterate through a list or access a list element directly\. So, it's not that cool as C\+\+ or JavaScript with its _arguments_ :\)

```cpp
function sum() {
  ....
  for(var i=0; i < arguments.length; i++) 
    s += arguments[i]
}
```

## Conclusion

To sum it up, I'd like to say that C\+\+ and C\# are highly flexible languages as far as their grammar goes, and that's why they are convenient to use on the one hand, but don't protect you from typos on the other\. There is an established belief that in C\# it's impossible to make such mistakes as in C\+\+, but it's just not true\. This article demonstrates rather interesting language features, but the bulk of errors in C\# has nothing to do with them; instead, they typically occur when writing common _if_\-inductions, like in [Infragistics](https://pvs-studio.com/en/blog/posts/csharp/0375/) project\. For example:

```cpp
public bool IsValid
{
get {
  var valid = 
    double.IsNaN(Latitude) || double.IsNaN(Latitude) ||
    this.Weather.DateTime == Weather.DateTimeInitial;
  return valid;
 }
}
```

[V3001](https://pvs-studio.com/en/docs/warnings/v3001/) There are identical sub\-expressions 'double\.IsNaN\(Latitude\)' to the left and to the right of the '\|\|' operator\. WeatherStation\.cs 25

It is at points like this that human attention tends to weaken, which causes you later to waste a huge amount of time trying to track down "God\-knows\-what–God\-knows\-where"\. So don't miss the chance to protect yourself from bugs with the help of [PVS\-Studio](https://pvs-studio.com/en/pvs-studio/) static code analyzer\.