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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.
C# 6.0 and above have ?., the null-conditional member access operator (which is also called the Elvis operator by Microsoft and is not to be confused with the general usage of the term Elvis operator, whose equivalent in C# is ??, the null coalescing operator) and ?[], the null-conditional element access operator, which performs a null-safe call of an indexer get accessor.
The cast operator is not overloadable, but one can write a conversion operator method which lives in the target class. Conversion methods can define two varieties of operators, implicit and explicit conversion operators. The implicit operator will cast without specifying with the cast operator (()) and the explicit operator requires it to be used.
In object-oriented computer programming, a null object is an object with no referenced value or with defined neutral (null) behavior.The null object design pattern, which describes the uses of such objects and their behavior (or lack thereof), was first published as "Void Value" [1] and later in the Pattern Languages of Program Design book series as "Null Object".
In Gosu, the ?: operator returns the right operand if the left is null as well. In C#, the null-conditional operator, ?. is referred to as the "Elvis operator", [10] but it does not perform the same function. Instead, the null-coalescing operator?? does. In ColdFusion and CFML, the Elvis operator was introduced using the ?: syntax.
The null safety based in types appeared first in Ceylon, followed soon by TypeScript. The C# language implements compile-time null safety check since version 8. However, to stay compatible with older versions of the language, the feature is opt-in on a per project or per file basis.
I'm not sure if Perl's defined-or operator does the same thing like C#'s null coalescing operator, but any attempts to indentify JS's, Ruby's and Python's operators with // are wrong. The ||-operator works much the same in Perl and JS, whenever the Left-Hand-Side has a value which is FALSE in boolean context, the Right-H-S will be returned.
The following example illustrates the different behavior. In C#, the lifted*operator propagates the null value of the operand; in Java, unboxing the null reference throws an exception. Not all C# lifted operators have been defined to propagate null unconditionally, if one of the operands is null.