Editing Iterator (section)

=== MATLAB ===
[[MATLAB]] supports both external and internal implicit iteration using either "native" arrays or <code>cell</code> arrays. In the case of external iteration where the onus is on the user to advance the traversal and request next elements, one can define a set of elements within an array storage structure and traverse the elements using the <code>for</code>-loop construct. For example,

<syntaxhighlight lang="matlab">
% Define an array of integers
myArray = [1,3,5,7,11,13];

for n = myArray
   % ... do something with n
   disp(n)  % Echo integer to Command Window
end
</syntaxhighlight>

traverses an array of integers using the <code>for</code> keyword.

In the case of internal iteration where the user can supply an operation to the iterator to perform over every element of a collection, many built-in operators and MATLAB functions are overloaded to execute over every element of an array and return a corresponding output array implicitly. Furthermore, the <code>arrayfun</code> and <code>cellfun</code> functions can be leveraged for performing custom or user defined operations over "native" arrays and <code>cell</code> arrays respectively. For example,

<syntaxhighlight lang="matlab">
function simpleFun
% Define an array of integers
myArray = [1,3,5,7,11,13];

% Perform a custom operation over each element 
myNewArray = arrayfun(@(a)myCustomFun(a),myArray);

% Echo resulting array to Command Window
myNewArray

function outScalar = myCustomFun(inScalar)
% Simply multiply by 2
outScalar = 2*inScalar;
</syntaxhighlight>

defines a primary function <code>simpleFun</code> that implicitly applies custom subfunction <code>myCustomFun</code> to each element of an array using built-in function <code>arrayfun</code>.

Alternatively, it may be desirable to abstract the mechanisms of the array storage container from the user by defining a custom object-oriented MATLAB implementation of the Iterator Pattern. Such an implementation supporting external iteration is demonstrated in MATLAB Central File Exchange item [http://www.mathworks.com.au/matlabcentral/fileexchange/25225 Design Pattern: Iterator (Behavioral)]. This is written in the new class-definition syntax introduced with MATLAB software version 7.6 (R2008a) and features a one-dimensional <code>cell</code> array realization of the [[List (computing)|List Abstract Data Type]] (ADT) as the mechanism for storing a heterogeneous (in data type) set of elements. It provides the functionality for explicit forward [[List (computing)|List]] traversal with the <code>hasNext()</code>, <code>next()</code> and <code>reset()</code> methods for use in a <code>while</code>-loop.