Excerpts from ECMA bible, verse 334 :
12.2 Default values
The default value of a variable depends on the type of the variable and is determined as follows:
- For a variable of a value-type, the default value is the same as the value computed by the value-type's default constructor (§11.1.1).
- For a variable of a reference-type, the default value is
null
.
[Note: Initialization to default values is typically done by having the memory manager or garbage collector
initialize memory to all-bits-zero before it is allocated for use. For this reason, it is convenient to use all-bitszero
to represent the null reference. end note]
The default value of a nullable type is an instance for which the HasValue
property is false
. Referencing the
Value property of a default value of a nullable type results in an exception of type
System.InvalidOperationException
. The default value is also known as the null value of the
nullable type. An implicit conversion exists from the null type (§11.2.7) to any nullable type, and this
conversion produces the null value of the type.
18.3.4 Default values
As described in §12.2, several kinds of variables are automatically initialized to their default value when
they are created. For variables of class types and other reference types, this default value is null. However,
since structs are value types that cannot be null, the default value of a struct is the value produced by
setting all value type fields to their default value and all reference type fields to null.
Example: Referring to the Point struct declared above, the example
Point[] a = new Point[100];
initializes each Point in the array to the value produced by setting the x and y fields to zero.
The default value of a struct corresponds to the value returned by the default constructor of the struct
(§11.1.1). Unlike a class, a struct is not permitted to declare a parameterless instance constructor. Instead, every struct implicitly has a parameterless instance constructor, which always returns the value that results
from setting all value type fields to their default value and all reference type fields to null.
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
.
Amen
You could download the holy book (version 4.0) directly from microsoft website.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…