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A map, sometimes referred to as a dictionary, consists of a key/value pair. The key is used to order the sequence, and the value is somehow associated with that key. For example, a map might contain keys representing every unique word in a text and values representing the number of times that word appears in the text.
Thus, when iterating through it, a map object returns keys in order of insertion. The following demonstrates enumeration using a for-loop: // loop through the collection and display each entry. for ( const [ name , number ] of phoneBook ) { console . log ( `Phone number for ${ name } is ${ number } ` ); }
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.
In object-oriented programming, the iterator pattern is a design pattern in which an iterator is used to traverse a container and access the container's elements. The iterator pattern decouples algorithms from containers; in some cases, algorithms are necessarily container-specific and thus cannot be decoupled.
The order of enumeration is always deterministic for a given set of keys by sorting. This is the case for tree-based implementations, one representative being the <map> container of C++. [16] The order of enumeration is key-independent and is instead based on the order of insertion.
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.
ParaSail also supports filters on iterators, and the ability to refer to both the key and the value of a map. Here is a forward iteration over the elements of "My_Map" selecting only elements where the keys are in "My_Set":
This is done in a single pass through the data range. As no elements are actually removed and the container retains the same size, the tail of the array has a length equal to the number of "removed" items; these items remain in memory but in an unspecified state.