C# LANGUAGE SPECIFICATION

1In effect, the rank-specifiers are read from left to right before the final non-array element type. [Example:

2The type int[][,,][,] is a single-dimensional array of three-dimensional arrays of two-dimensional

3arrays of int. end example]

4At run-time, a value of an array type can be null or a reference to an instance of that array type or a

5covariant array type, as described in §19.5.

619.1.1 The System.Array type

7The type System.Array is the abstract base type of all array types. An implicit reference conversion

8(§13.1.4) exists from any array type to System.Array and to any interface type implemented by

9System.Array. An explicit reference conversion (§13.2.3) exists from System.Array and any interface

10type implemented by System.Array to any array type. System.Array is not itself an array-type. Rather,

11it is a class-type from which all array-types are derived.

12At run-time, a value of type System.Array can be null or a reference to an instance of any array type.

1319.2 Array creation

14Array instances are created explicitly by array-creation-expressions (§14.5.10.2) or by field or local variable

15declarations that include an array-initializer (§19.6). Array instances can also be created implicitly by

16invoking a method in its expanded form (§14.4.1).

17When an array instance is created, the rank and length of each dimension are established and then remain

18constant for the entire lifetime of the instance. In other words, it is not possible to change the rank of an

19existing array instance, nor is it possible to resize its dimensions.

20An array instance is always of an array type. The System.Array type is an abstract type that cannot be

21instantiated.

22Elements of arrays created by array-creation-expressions are always initialized to their default value

23(§12.2).

2419.3 Array element access

25Array elements are accessed using element-access expressions (§14.5.6.1) of the form A[I1, I2, …, IN],

26where A is an expression of an array type and each IX is an expression of type int, uint, long, ulong, or

27of a type that can be implicitly converted to one or more of these types. The result of an array element access

28is a variable, namely the array element selected by the indices.

29The elements of an array can be enumerated using a foreach statement (§15.8.4).

3019.4 Array members

31Every array type inherits the members declared by the System.Array type.

3219.5 Array covariance

33For any two reference-types A and B, if an implicit reference conversion (§13.1.4) or explicit reference

34conversion (§13.2.3) exists from A to B, then the same reference conversion also exists from the array type

35A[R] to the array type B[R], where R is any given rank-specifier (but the same for both array types). This

36relationship is known as array covariance. Array covariance, in particular, means that a value of an array

37type A[R] might actually be a reference to an instance of an array type B[R], provided an implicit reference

38conversion exists from B to A.

39Because of array covariance, assignments to elements of reference type arrays include a run-time check

40which ensures that the value being assigned to the array element is actually of a permitted type (§14.13.1).

41[Example:

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C# LANGUAGE SPECIFICATION

119.7 Array initializers

2Array initializers can be specified in field declarations (§17.4), local variable declarations (§15.5.1), and

3array creation expressions (§14.5.10.2):

4array-initializer:

13An array initializer consists of a sequence of variable initializers, enclosed by “{”and “}” tokens and

14separated by “,” tokens. Each variable initializer is an expression or, in the case of a multi-dimensional

15array, a nested array initializer.

16The context in which an array initializer is used determines the type of the array being initialized. In an array

17creation expression, the array type immediately precedes the initializer. In a field or variable declaration, the

18array type is the type of the field or variable being declared. When an array initializer is used in a field or

19variable declaration, [Example: such as:

20int[] a = {0, 2, 4, 6, 8};

21end example] it is simply shorthand for an equivalent array creation expression: [Example:

22int[] a = new int[] {0, 2, 4, 6, 8};

23end example]

24For a single-dimensional array, the array initializer shall consist of a sequence of expressions that are

25assignment compatible with the element type of the array. The expressions initialize array elements in

26increasing order, starting with the element at index zero. The number of expressions in the array initializer

27determines the length of the array instance being created. [Example: The array initializer above creates an

28int[] instance of length 5 and then initializes the instance with the following values:

29a[0] = 0; a[1] = 2; a[2] = 4; a[3] = 6; a[4] = 8;

30end example]

31For a multi-dimensional array, the array initializer shall have as many levels of nesting as there are

32dimensions in the array. The outermost nesting level corresponds to the leftmost dimension and the

33innermost nesting level corresponds to the rightmost dimension. The length of each dimension of the array is

34determined by the number of elements at the corresponding nesting level in the array initializer. For each

35nested array initializer, the number of elements shall be the same as the other array initializers at the same

36level. [Example: The example:

37int[,] b = {{0, 1}, {2, 3}, {4, 5}, {6, 7}, {8, 9}};

38creates a two-dimensional array with a length of five for the leftmost dimension and a length of two for the

39rightmost dimension:

40int[,] b = new int[5, 2];

41and then initializes the array instance with the following values:

42b[0, 0] = 0; b[0, 1] = 1;

43b[1, 0] = 2; b[1, 1] = 3;

44b[2, 0] = 4; b[2, 1] = 5;

45b[3, 0] = 6; b[3, 1] = 7;

46b[4, 0] = 8; b[4, 1] = 9;

47end example]

332