What does default(object); do in C#?

c# default(t) returns null
default value c# method
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c# default exclamation mark
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Googling is only coming up with the keyword, but I stumbled across some code that says

MyVariable = default(MyObject);

and I am wondering what it means...

default value expressions, int a = default(int);. Beginning with C# 7.1, you can use the default literal to initialize a variable with the default value of its type: C# Copy. For some classes, the default behavior of Object 's clone () method works just fine. If, however, an object contains a reference to an external object, say ObjExternal, you may need to override clone () to get correct behavior. Otherwise, a change in ObjExternal made by one object will be visible in its clone also.

default keyword will return null for reference types and zero for numeric value types.

For structs, it will return each member of the struct initialized to zero or null depending on whether they are value or reference types.

from MSDN

Simple Sample code :<br>
    class Foo
    {
        public string Bar { get; set; }
    }

    struct Bar
    {
        public int FooBar { get; set; }
        public Foo BarFoo { get; set; }
    }

    public class AddPrinterConnection
    {
        public static void Main()
        {

            int n = default(int);
            Foo f = default(Foo);
            Bar b = default(Bar);

            Console.WriteLine(n);

            if (f == null) Console.WriteLine("f is null");

            Console.WriteLine("b.FooBar = {0}",b.FooBar);

            if (b.BarFoo == null) Console.WriteLine("b.BarFoo is null");

        }
    }

OUTPUT:

0
f is null
b.FooBar = 0
b.BarFoo is null

Default values of C# types, Default represents default value of T parameter in generics intructions. In several cases Default keyword can make our work easier and can make the code safer​. WriteLine();; ChangeValues(ref a, ref b);; System.Console. Another use case for Default(T) could be for reset instance of generics objects. In the Default Value property box, type the following: [control_name].ItemData(n) In this case, control_name is the name of the list box or combo box control, and n is the number of the list item that you want to make the default. If you don't know the name of the control, look at the value in the Name property, located at the top of the

Default(T) In Generics, If you don't provide a constructor for your class, C# creates one by default that instantiates the object and sets member variables to the default values as listed in the Default Values Table. The drawback of a default constructor is that every instance of the class will be initialized to the same values and it WriteLine(obj.a​);. The default toString() method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@’, and the unsigned hexadecimal representation of the hash code of the object.

Specifies the default value of the type parameter.This will be null for reference types and zero for value types.

See default

Default Values | Understanding C# Types, C(0) creates an object of class C whose identifier is 0. The initial value of an attribute can be specified by the user when an object is created. The object identifier O. attr of a newly created default object is formed from its attribute name attr,  The default implementation of GetHashCode() for reference types returns a hash code that is equivalent to the one returned by the GetHashCode(Object) method. You can override GetHashCode() for immutable reference types.

The default keyword returns the "default" or "empty" value for a variable of the requested type.

For all reference types (defined with class, delegate, etc), this is null. For value types (defined with struct, enum, etc) it's an all-zeroes value (for example, int 0, DateTime 0001-01-01 00:00:00, etc).

It's mostly used with generic code that can be applied to both reference and value types, because you can't assign null to a value type variable.

Why is the default value of the string type null instead of an empty , Program to calculate Electricity Bill · How to Execute C# Program on cmd (​command-line)? · How to Read and Write a Text File in C#? Therefore the Object class methods are available to all C# classes. It will return the name class. Console.WriteLine(t1.Name);. // It will return the By default Namespace is System. It converts an object to its string representation so that it is suitable for display. (For information about formatting support in the .NET Framework, see Formatting Types.) Default implementations of the Object.ToString method return the fully qualified name of the object's type.

C# DateTime Usage – bitScry, In some cases, one can return a “default” or “neutral” object, such as Collections. code base: Pattern: Null Object If many clients of a class C check for null and  Object.prototype.constructor Specifies the function that creates an object's prototype. Object.prototype.__proto__ Points to the object which was used as prototype when the object was instantiated. Object.prototype.__noSuchMethod__ Allows a function to be defined that will be executed when an undefined object member is called as a method.

All About Constructors In C#, We will now show how the model can easily be extended to support works: every object (c in the figure), as seen before, is represented by a proxy that references So, the default class proxy is needed because inserting a class-​wide aspect  Default methods enable you to add new functionality to existing interfaces and ensure binary compatibility with code written for older versions of those interfaces. In particular, default methods enable you to add methods that accept lambda expressions as parameters to existing interfaces. This section demonstrates how the Comparator interface

C#, It returns the default value when the object is not initialized. For example, we all In case of Generic object when the type is undefined, we can use default to assign specific value to the object. Let us look at return default(T);. After the default properties are set on an object (assuming they are set), when you output an object to the console without any Format-verb cmdlets at the end of the pipeline, the PowerShell formatting engine looks in the format data it has loaded and finds the first format data specification whose object type matches the one of the types in

Comments
  • If I create class Foo with property int n. Can I "overload" default to make it set n to say 5 instead of 0?
  • @The Machine Charmer: No. You can't overload default.
  • Isn't int foo = default(int); the same was int foo;? Ie don't uninitialized ints default to having the same value as default(int)?
  • @AdamParkin that depends on whether you are talking about fields vs locals; yes, fields initialize to a zero-d space, the same as default(...); locals do not have default values (although technically, .locals init in IL means that they will again default to zero, but you need to use unsafe mechanisms to observe it)
  • "It returns the empty (psuedo-null) value that... that what? Looks like the sentence wasn't finished.