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  • How does initializing inherited members inside base class constructor reduce the calls to…?

    - by flockofcode
    I’ve read that instead of initializing inherited members ( _c1 in our example ) inside derived constructor: class A { public int _c; } class B:A { public B(int c) { _c = c; } } we should initialize them inside base class constructor, since that way we reduce the calls to inherited members ( _c ): class A { public A(int c) { _c = c; } public int _c; } class B:A { public B(int c) : base(c) { } } If _c field is initialized inside base constructor, the order of initialization is the following: 1) First the field initializers of derived class B are called 2) Then field initializers of base class A are called (at this point _c is set to value 0) 3) B’s constructor is called, which in turn calls A’s custom constructor 4) _c field gets set to value of a parameter c ( inside A’s custom constructor ) 5) Once A’s custom constructor returns, B’s constructor executes its code. If _c field is initialized inside B's constructor, the order of initialization is the following: 1) First the field initializers of a derived class B are called 2) Then field initializers of a base class A are called(at this point _c is set to value 0) 3) B’s constructor is called, which in turn calls A’s default constructor 4) Once A’s custom constructor returns, B’s constructor sets _c field to a value of parameter c As far as I can tell, in both cases was _c called two times, so how exactly did we reduce calls to inherited member _c? thanx

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  • Can't add/remove items from a collection while foreach is iterating over it

    - by flockofcode
    If I make my own implementation of IEnumerator interface, then I am able ( inside foreach statement )to add or remove items from a albumsList without generating an exception.But if foreach statement uses IEnumerator supplied by albumsList, then trying to add/delete ( inside the foreach )items from albumsList will result in exception: class Program { static void Main(string[] args) { string[] rockAlbums = { "rock", "roll", "rain dogs" }; ArrayList albumsList = new ArrayList(rockAlbums); AlbumsCollection ac = new AlbumsCollection(albumsList); foreach (string item in ac) { Console.WriteLine(item); albumsList.Remove(item); //works } foreach (string item in albumsList) { albumsList.Remove(item); //exception } } class MyEnumerator : IEnumerator { ArrayList table; int _current = -1; public Object Current { get { return table[_current]; } } public bool MoveNext() { if (_current + 1 < table.Count) { _current++; return true; } else return false; } public void Reset() { _current = -1; } public MyEnumerator(ArrayList albums) { this.table = albums; } } class AlbumsCollection : IEnumerable { public ArrayList albums; public IEnumerator GetEnumerator() { return new MyEnumerator(this.albums); } public AlbumsCollection(ArrayList albums) { this.albums = albums; } } } a) I assume code that throws exception ( when using IEnumerator implementation A supplied by albumsList ) is located inside A? b) If I want to be able to add/remove items from a collection ( while foreach is iterating over it), will I always need to provide my own implementation of IEnumerator interface, or can albumsList be set to allow adding/removing items? thank you

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  • Checked and Unchecked operators don't seem to be working when...

    - by flockofcode
    1) Is UNCHECKED operator in effect only when expression inside UNCHECKED context uses an explicit cast ( such as byte b1=unchecked((byte)2000); ) and when conversion to particular type can happen implicitly? I’m assuming this since the following expression throws a compile time error: byte b1=unchecked(2000); //compile time error 2) a) Do CHECKED and UNCHECKED operators work only when resulting value of an expression or conversion is of an integer type? I’m assuming this since in the first example ( where double type is being converted to integer type ) CHECKED operator works as expected: double m = double.MaxValue; b=checked((byte)m); // reports an exception , while in second example ( where double type is being converted to a float type ) CHECKED operator doesn’t seem to be working. since it doesn't throw an exception: double m = double.MaxValue; float f = checked((float)m); // no exception thrown b) Why don’t the two operators also work with expressions where type of a resulting value is of floating-point type? 2) Next quote is from Microsoft’s site: The unchecked keyword is used to control the overflow-checking context for integral-type arithmetic operations and conversions I’m not sure I understand what exactly have expressions and conversions such as unchecked((byte)(100+200)); in common with integrals? Thank you

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  • Why are member constants available even if there are no instances of a its class?

    - by flockofcode
    1) Why are member constants available even if there are no instances of a its class? 2) Is the only reason why constant expressions need to be fully evaluated at compile time due to compiler replacing constant variable with literal value? 3) Since string is also an object, I would think the following would produce an error, but it doesn’t. Why? class A { const string b = “it works”; } thank you

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  • IS operator behaving a bit strangely

    - by flockofcode
    1) According to my book, IS operator can check whether expression E (E is type) can be converted to the target type only if E is either a reference conversion, boxing or unboxing. Since in the following example IS doesn’t check for either of the three types of conversion, the code shouldn’t work, but it does: int i=100; if (i is long) //returns true, indicating that conversion is possible l = i; 2) a) B b; A a = new A(); if (a is B) b = (B)a; int i = b.l; class A { public int l = 100; } class B:A { } The above code always causes compile time error “Use of unassigned variable”. If condition a is B evaluates to false, then b won’t be assigned a value, but if condition is true, then it will. And thus by allowing such a code compiler would have no way of knowing whether the usage of b in code following the if statement is valid or not ( due to not knowing whether a is b evaluates to true or false) , but why should it know that? Intsead why couldn’t runtime handle this? b) But if instead we’re dealing with non reference types, then compiler doesn’t complain, even though the code is identical.Why? int i = 100; long l; if (i is long) l = i; thank you

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  • Is the following array really multidimensional?

    - by flockofcode
    Book I’ learning from claims that intArray has two dimensions. But since calling intArray.GetLength(1) will result in an IndexoutOfRange exception, couldn’t we claim that unlike rectangular arrays, intArray isn’t really multidimensional and thus has only one dimension? int[][] intArray=new int[3][]; thank you

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  • Doesn't this defeat the whole purpose of having read-only properties?

    - by flockofcode
    I know how to use properties and I understand that they implicitly call underlying get and set accessors, depending on whether we are writing to or reading from a property. static void Main(string[] args) { A a = new A(); (a.b).i = 100; } class A { private B _b = new B(); public B b { get { return _b; } } } class B { public int i; } What code (a.b).i = 100; essentially does is that first property’s get accessor returns a reference to an object _b, and once we have this reference, we are able to access _b’s members and change their values. Thus, in our example, having read only property only prevents outside code from changing the value of a reference variable _b, but it doesn’t prevent outside code from accessing _b’s members. So it seems that property can only detect whether we are trying to read from or write to a variable ( in our case variable _b ) located on the stack, while it’s not able to detect whether we’re trying to also write to members of an object to which the variable on the stack ( assuming this variable is of reference type ) points to. a) But doesn’t that defeat the whole purpose of having read-only properties? Wouldn’t it be more effective if properties had the ability to also detect whether we’re trying to access members of an object returned by get accessor( assuming backing field is of a reference type )? thank you

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