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When being inserted to a dictionary, the value object receives a retain message to increase its reference count. The value object will receive the release message when it will be deleted from the dictionary (either explicitly or by adding to the dictionary a different object with the same key).
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.
In mathematical terms, an associative array is a function with finite domain. [1] It supports 'lookup', 'remove', and 'insert' operations. The dictionary problem is the classic problem of designing efficient data structures that implement associative arrays. [2] The two major solutions to the dictionary problem are hash tables and search trees.
In C#, a class is a reference type while a struct (concept derived from the struct in C language) is a value type. [5] Hence an instance derived from a class definition is an object while an instance derived from a struct definition is said to be a value object (to be precise a struct can be made immutable to represent a value object declaring attributes as readonly [6]).
This could be modeled in an object-oriented implementation by a "Person object" with an attribute/field to hold each data item that the entry comprises: the person's name, a list of phone numbers, and a list of addresses. The list of phone numbers would itself contain "PhoneNumber objects" and so on.
In the following tables, lower case letters such as a and b represent literal values, object/variable names, or l-values, as appropriate. R, S and T stand for a data type, and K for a class or enumeration type. Some operators have alternative spellings using digraphs and trigraphs or operator synonyms.
The null coalescing operator is a binary operator that is part of the syntax for a basic conditional expression in several programming languages, such as (in alphabetical order): C# [1] since version 2.0, [2] Dart [3] since version 1.12.0, [4] PHP since version 7.0.0, [5] Perl since version 5.10 as logical defined-or, [6] PowerShell since 7.0.0, [7] and Swift [8] as nil-coalescing operator.
This feature was eventually removed, and now this in C++ is an r-value. [9] Early versions of C++ did not include references and it has been suggested that had they been so in C++ from the beginning, this would have been a reference, not a pointer. [10] C++ lets objects destroy themselves with the source code statement: delete this.