Spar - array expressions

An array expression is a shorthand notation for the construction of a (partial) copy of an array. For example, the following code will first construct an array a, and then construct a copy of the first row of a, and assign it to v:

int[*,*] a = {{0,1,2},{3,4,5},{6,7,8}};
int[*] v = a[0,0:a.getSize(1)];

Note that v is a copy, so subsequent assignments to elements of v are not visible in a. Contrary to array range notations in many other languages, the top of the specified range is the first element not to be included.

The usual range shorthands apply: if no start of the range is given, 0 is assumed, and if no end of the range is given, the size in that dimension is assumed. Thus the declaration of v in the previous code fragment could be written as:

int[*] v = a[0,:];

Array statements

Array statements are a shorthand notation for a foreach statement that is executed for all elements of a selected range. For example, the code fragment

Block[*,*] a = new Block[5,7];
a[:,:].init();

will invoke the method init on all elements of Block array a. Since this is equivalent to a erm{foreach} statement, the init method of each of the array elements is not invoked in a prescribed order.

Similarly, array assignments are a shorthand for repeated assignments. For example:

int[*,*] a = new int[5,7];

a[:,:] = 0;

will zero the entire array a.

The expression at the right-hand side of the assignment will be evaluated only once. Thus,

int ix = 0;
int[*,*] a = new int[5,7];

a[:,:] = ix++;

will again zero the entire array a, and will leave ix with the value 1.

Last but not least, array assignments may contain an array at the right-hand side, instead of a single element. In that case every iteration of the foreach will use the implicit iteration vector as index for every assignment.

For example:

int[*,*] a = new int[5,7];
int[*,*] b = new int a.getSize();

b[:,:] = 1;
a[:,:] = b;

will copy b into a. The last statement could also be written as:

a[:,:] = b[:,:];

but a naive compiler would first create a copy of b, and leave it for the garbage collector.

Array statements never change the size of the array they work on. Any access that is out of bounds is detected at compile-time or run-time, and causes an error message or an IndexOutOfBoundsException exception.

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