Spar - arrays

An array type is written as the name of an element type, followed by a number of abstract shape specifications. For example:

int[*] v;               // A 1-dimensional array
int[*,*] A;             // A 2-dimensional array

For compatibility with Java, Spar also allows Java-style declarations of one-dimensional arrays:

int[] n;                // A 1-dimensional array

This is a special case.

Here are some examples of declarations of array variables that create array objects:

int a[*] = new int[4];
short b[*,*] = new short[6,8];
int sq[*] = { 1, 4, 9, 16, 25, 36 };
real ident[*,*] = {{1,0,0}, {0,1,0}, {0,0,1}};
real vv[*][*] = {{1,0,0}, {0,1,0}, {0,0,1}};
String[] aos = { "array", "of", "string" };

Note that ident and vv have the same initialization expression, but they are not equivalent. The first is a two-dimensional array, the second is a one-dimensional array of one-dimensional arrays.

A component of an array is accessed by an expression that consists of an array reference followed by an int vector expression, as in: A[i,j]. All arrays start at element 0. A one-dimensional array with length n can be indexed by the integers 0 to n-1.

For example, the following assigns 2 to array element [2,3] of array A.

int[*,*] A = new int[9,9]; // A 2-dim array
A[2,3] = 2;                // An array access

This looks very similar to array access in other languages, but in the case of Spar this is a special case of a more general access construct, where arbitrary vector expressions can be used to access an array. Since any vector expression can be used, very powerful access expressions are possible. This is demonstrated in the following code:

int[*,*] A = new int[9,9];  // A 2-dim array
[int^2] v = [1,1];          // A vector of 2 elm.
A@v = 3;                   // A[1,1] = 3
A@(3*v) = 4;               // A[3,3] = 4 

As much as possible, array accesses are checked for bounds violations at compile time. If the array access cannot be checked at compile time, an index that is out of bounds causes an IndexOutOfBoundsException to be thrown.

Last modified Sat May 13 15:50:56 2017 UT by Kees van Reeuwijk.