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They can be used to iterate over any object that implements the NSFastEnumeration protocol, including NSArray, NSDictionary (iterates over keys), NSSet, etc. NSArray * a = [ NSArray new ]; // Any container class can be substituted for ( id obj in a ) { // Dynamic typing is used.
Some object-oriented languages such as C#, C++ (later versions), Delphi (later versions), Go, Java (later versions), Lua, Perl, Python, Ruby provide an intrinsic way of iterating through the elements of a collection without an explicit iterator. An iterator object may exist, but is not represented in the source code.
The foreach statement is derived from the for statement and makes use of a certain pattern described in C#'s language specification in order to obtain and use an enumerator of elements to iterate over. Each item in the given collection will be returned and reachable in the context of the code block.
Python uses the following syntax to express list comprehensions over finite lists: S = [ 2 * x for x in range ( 100 ) if x ** 2 > 3 ] A generator expression may be used in Python versions >= 2.4 which gives lazy evaluation over its input, and can be used with generators to iterate over 'infinite' input such as the count generator function which ...
In computer science, a generator is a routine that can be used to control the iteration behaviour of a loop.All generators are also iterators. [1] A generator is very similar to a function that returns an array, in that a generator has parameters, can be called, and generates a sequence of values.
Folds can be regarded as consistently replacing the structural components of a data structure with functions and values. Lists, for example, are built up in many functional languages from two primitives: any list is either an empty list, commonly called nil ([]), or is constructed by prefixing an element in front of another list, creating what is called a cons node ( Cons(X1,Cons(X2,Cons ...
a b c A counting loop can be simulated by iterating over an incrementing list or generator, for instance, Python's range(). ... FileStream stm = null; // C# example ...
C# 2.0 added semi-coroutine functionality through the iterator pattern and yield keyword. [44] [45] C# 5.0 includes await syntax support. In addition: The MindTouch Dream REST framework provides an implementation of coroutines based on the C# 2.0 iterator pattern.