Array base class


This pod file documents the Array base class usage. For implementation details you should look inside the class file, found at src/pmc/array.pmc in the parrot source code.


  new P0, 'Array'   # initialize P0 as an array

  set I0, P0        # set I0 to the size of the array in P0
  set P0, 2         # set the size of the array in P0 to 2

  set P0[0], "foo"  # put "foo" into the array at position 0
  set I1, P0[1]     # get an integer value from the entry 
                    # at array position 1

  defined I2, P0[1] # is the value at position 1 defined?
  exists  I3, P0[0] # is there an element at position 0?


Creation ^

As with any other PMC, the following line creates an array PMC in register P0:

  new P0, 'Array'

Array sizes ^

You can retrieve the size of the array using

  set I0, P0

This will put the size of the array in register P0 into I0. In the same way, assigning an integer directly to the array sets the size of the array. For instance:

  new P0, 'Array'
  set P0, 2

creates a new Array (with default size 0) and then expands the size of the array to two.

Arrays do not automatically resize themselves when you access out-of-bounds elements. This means that you must remember to size an Array appropriately before storing anything in it.

Accessing elements ^

Elements are accessed using indexes, as in any programming language.

The following code initializes an array in P0 with size two, and sets the first position to the integer -8 and second position to the floating point number 3.1415.

  new P0, 'Array'
  set P0, 2

  set P0[0], -8
  set P0[1], 3.1415

You can also assign directly from registers; for instance:

  new P0, 'Array'
  set P0, 2

  set I0, -8
  set N0, 3.1415

  set P0[0], I0
  set P0[1], N0

leaves P0 in the same state as in the previous code snippet.

To retrieve elements, we use the same syntax:

  set N1, P0[1]
  set I1, P0[0]

Those two lines retrieve the values from the array back into registers.

The value stored at a given position is not fixed; it can be changed simply by assigning a new value:

  set P0[1], "A string"

Accessing an out-of-bounds array element raises an exception; if you want an Array that will automatically resize, then use a ResizablePMCArray.

You can test if there is a defined element at an array position by using

  defined I0, P0[1]

for the position you want to test. On the other hand, if you only want to test whether a given element exists (rather than whether it is defined), then use the exists op instead:

  exists I0, P0[0]


Explain a little more which exception will be raised in case you access a out-of-bounds index on the array (as soon we have exceptions).