ECMA-334: 11.1.2 Default constructors

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C# Language Specification

11. Types 11.1 Value types 11.1.1 System.ValueType type 11.1.2 Default constructors 11.1.3 Struct types 11.1.4 Simple types 11.1.5 Integral types 11.1.6 Floating point types 11.1.7 decimal type 11.1.8 bool type 11.1.9 Enumeration types

© 2006 ECMA International

11.1.2 Default constructors

All value types implicitly declare a public parameterless instance constructor called the default constructor. The default constructor returns a zero-initialized instance known as the default value for the value type:

• For all simple-types, the default value is the value produced by a bit pattern of all zeros:

• For sbyte, byte, short, ushort, int, uint, long, and ulong, the default value is 0.

• For char, the default value is '\x0000'.

• For float, the default value is 0.0f.

• For double, the default value is 0.0d.

• For decimal, the default value is 0m.

• For bool, the default value is false.

• For an enum-type E, the default value is 0.

• For a struct-type, the default value is the value produced by setting all value type fields to their default value and all reference type fields to null.

• For a nullable type, the default value is one for which HasValue returns false.

Like any other instance constructor, the default constructor of a value type is invoked using the new operator. [Note: For efficiency reasons, this requirement is not intended to actually have the implementation generate a constructor call. For value types, the default value expression (§14.5.14) produces the same result as using the default constructor. end note] [Example: In the code below, variables i, j and k are all initialized to zero.

class A
{
  void F()
  {
    int i = 0;
    int j = new int();
    int k = default(int);
  }
}

end example]

Because every value type implicitly has a public parameterless instance constructor, it is not possible for a struct type to contain an explicit declaration of a parameterless constructor. A struct type is however permitted to declare parameterized instance constructors (§18.3.8).