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The iteration form of the Eiffel loop can also be used as a boolean expression when the keyword loop is replaced by either all (effecting universal quantification) or some (effecting existential quantification). This iteration is a boolean expression which is true if all items in my_list have counts greater than three:
the Add method, which adds a key and value and throws an exception if the key already exists in the dictionary; assigning to the indexer, which overwrites any existing value, if present; and; assigning to the backing property of the indexer, for which the indexer is syntactic sugar (not applicable to C#, see F# or VB.NET examples).
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
The loop counter is used to decide when the loop should terminate and for the program flow to continue to the next instruction after the loop. A common identifier naming convention is for the loop counter to use the variable names i , j , and k (and so on if needed), where i would be the most outer loop, j the next inner loop, etc.
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 .
In PHP and R, all arrays can be associative, except that the keys are limited to integers and strings. In JavaScript (see also JSON), all objects behave as associative arrays with string-valued keys, while the Map and WeakMap types take arbitrary objects as keys. In Lua, they are used as the primitive building block for all data structures.
Single-value containers store each object independently. Objects may be accessed directly, by a language loop construct (e.g. for loop) or with an iterator. An associative container uses an associative array, map, or dictionary, composed of key-value pairs, such that each key appears at most once in the container. The key is used to find the ...
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 ...