As the preceding example shows, you also use square brackets when you declare an array type or instantiate an array instance. The [] operator is also considered a non-overloadable operator. You also use square brackets to specify attributes: Available in C# 6 and later, a null-conditional operator applies a member access, ?., or element access, ? operator evaluates its left-hand operand no more than once, guaranteeing that it cannot be changed to null after being verified as non-null. [], operation to its operand only if that operand evaluates to non-null; otherwise, it returns null. As the preceding example shows, expression ^e is of the System.Index type. The right-hand operand is an exclusive end of a range. You can use the following operators and expressions when you access a type member: You use the . The null-conditional operators are short-circuiting. Available in C# 8.0 and later, the .. operator specifies the start and end of a range of indices as its operands. That is. token to access a member of a namespace or a type, as the following examples demonstrate: Use a using directive to make the use of qualified names optional. The following example demonstrates how to call a method, with or without arguments, and invoke a delegate: You also use parentheses when you invoke a constructor with the new operator. Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support.
If a evaluates to non-null, the result of a?.x or a? If a evaluates to null, the result of a?.x or a? The following examples demonstrate the usage of the ?. The left-hand operand is an inclusive start of a range. You also use parentheses to adjust the order in which to evaluate operations in an expression. That is, if one operation in a chain of conditional member or element access operations returns null, the rest of the chain doesn't execute. Cast expressions, which perform explicit type conversions, also use parentheses. Available in C# 8.0 and later, the ^ operator indicates the element position from the end of a sequence. Square brackets, [], are typically used for array, indexer, or pointer element access. The following example demonstrates how to access array elements: If an array index is outside the bounds of the corresponding dimension of an array, an IndexOutOfRangeException is thrown. The following example uses the .NET Dictionary
For more information, see Indices and ranges. Use the ?. [x] would throw the same exception for non-null a. operator, numbers?.Length < 2 evaluates to false when numbers is null. If a.x or a[x] is of a non-nullable value type T, a?.x or a? to specify an alternative expression to evaluate in case the result of a null-conditional operation is null. For example, ^1 points to the last element of a sequence and ^length points to the first element of a sequence. You can also use the ^ operator with the range operator to create a range of indices. For information about pointer element access, see the Pointer element access operator [] section of the Pointer related operators article. [x] is the same as the result of a.x or a[x], respectively. is also known as the Elvis operator. Use conditional delegate call (style rule IDE1005). The ?. You can omit any of the operands of the .. operator to obtain an open-ended range: For more information, see Indices and ranges. Use parentheses, (), to call a method or invoke a delegate. If a.x or a[x] throws an exception, a?.x or a? [] operators: The first of the preceding two examples also uses the null-coalescing operator ?? For more information about arrays, see Arrays. In the following example, B is not evaluated if A evaluates to null and C is not evaluated if A or B evaluates to null: If A might be null but B and C would not be null if A is not null, you only need to apply the null-conditional operator to A: In the preceding example, B is not evaluated and C() is not called if A is null. For more information, see the following sections of the C# language specification: For more information about indices and ranges, see the feature proposal note. to a null-conditional expression, as the following example shows: In the preceding example, if you don't use the ?? Either of operands can be an index from the start or from the end of a sequence, as the following example shows: As the preceding example shows, expression a..b is of the System.Range type. to access an extension method. [x] is of the corresponding nullable value type T?. For a sequence of length length, ^n points to the element with offset length - n from the start of a sequence. The ., (), ^, and .. operators cannot be overloaded. operator to check if a delegate is non-null and invoke it in a thread-safe way (for example, when you raise an event), as the following code shows: That code is equivalent to the following code that you would use in C# 5 or earlier: That is a thread-safe way to ensure that only a non-null handler is invoked. If you need an expression of type T, apply the null-coalescing operator ?? You can also use . Use indexers to support indexing with user-defined types. Because delegate instances are immutable, no thread can change the object referenced by the handler local variable. In expression a..b, the results of a and b must be implicitly convertible to int or Index. [x] is null. [x] would throw an IndexOutOfRangeException. For example, if a is a non-null array instance and x is outside the bounds of a, a? For more information about indexers, see Indexers. Unlike array indices, which must be integer, the indexer parameters can be declared to be of any type. The null-conditional member access operator ?. and ?