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The macro is unhygienic: it declares a new variable in the existing scope which remains after the loop. One foreach macro cannot be defined that works with different collection types (e.g., array and linked list) or that is extensible to user types. C string as a collection of char
The J2SE 5.0 release of Java introduced the Iterable interface to support an enhanced for loop for iterating over collections and arrays. Iterable defines the iterator() method that returns an Iterator. [18]: 266 Using the enhanced for loop, the preceding example can be rewritten as
Java has had a standard interface for implementing iterators since its early days, and since Java 5, the "foreach" construction makes it easy to loop over objects that provide the java.lang.Iterable interface. (The Java collections framework and other collections frameworks, typically provide iterators for all collections.)
Loop invariants are used to monitor specific properties of a loop during successive iterations. Some programming languages, such as Eiffel contain native support for loop variants and invariants. In other cases, support is an add-on, such as the Java Modeling Language 's specification for loop statements in Java .
Maple has two forms of for-loop, one for iterating over a range of values, and the other for iterating over the contents of a container. The value range form is as follows: for i from f by b to t while w do # loop body od; All parts except do and od are optional. The for I part, if present, must come first.
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 ...
In object-oriented languages, string functions are often implemented as properties and methods of string objects. In functional and list-based languages a string is represented as a list (of character codes), therefore all list-manipulation procedures could be considered string functions.
In mathematics, iteration may refer to the process of iterating a function, i.e. applying a function repeatedly, using the output from one iteration as the input to the next. Iteration of apparently simple functions can produce complex behaviors and difficult problems – for examples, see the Collatz conjecture and juggler sequences .