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List comprehension is a syntactic construct available in some programming languages for creating a list based on existing lists. It follows the form of the mathematical set-builder notation (set comprehension) as distinct from the use of map and filter functions.
A list may contain the same value more than once, and each occurrence is considered a distinct item. A singly-linked list structure, implementing a list with three integer elements. The term list is also used for several concrete data structures that can be used to implement abstract lists, especially linked lists and arrays.
Queues allow the programmer to insert items in a certain order and retrieve those items in the same order. An example is a waiting list. The base interfaces for queues are called Queue. Dictionaries/Maps store references to objects with a lookup key to access the object's values. One example of a key is an identification card.
However, the compiler automatically transforms the code so that the list will "silently" receive objects, while the source code only mentions primitive values. For example, the programmer can now write list. add (3) and think as if the int 3 were added to the list; but, the compiler will have actually transformed the line into list. add (new ...
This PHP example shows interface implementations instead of subclassing (however, the same can be achieved through subclassing). The factory method can also be defined as public and called directly by the client code (in contrast to the previous Java example).
Unlike function and class names, variable names are case-sensitive. Both double-quoted ("") and heredoc strings allow the ability to embed a variable's value into the string. [13] As in C, variables may be cast to a specific type by prefixing the type in parentheses. PHP treats newlines as whitespace, in the manner of a free-form language.
For scalar values, once it has been assigned, the value of the final variable cannot change. For object values, the reference cannot change. For object values, the reference cannot change. This allows the Java compiler to "capture" the value of the variable at run-time and store a copy as a field in the inner class.
For example, in Java, C# and PHP, the keyword abstract is used. [ 26 ] [ 27 ] In C++ , an abstract class is a class having at least one abstract method given by the appropriate syntax in that language (a pure virtual function in C++ parlance).