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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.
expression 1, expression 2: Expressions with values of any type. If the condition is evaluated to true, the expression 1 will be evaluated. If the condition is evaluated to false, the expression 2 will be evaluated. It should be read as: "If condition is true, assign the value of expression 1 to result.
The detailed semantics of "the" ternary operator as well as its syntax differs significantly from language to language. A top level distinction from one language to another is whether the expressions permit side effects (as in most procedural languages) and whether the language provides short-circuit evaluation semantics, whereby only the selected expression is evaluated (most standard ...
If all terms in the sequence of conditionals are testing the value of a single expression (e.g., if x=0... else if x=1... else if x=2...), an alternative is the switch statement, also called case-statement or select-statement. Conversely, in languages that do not have a switch statement, these can be produced by a sequence of else if statements.
void Increment (ref int x, int dx = 1) {x += dx;} int x = 0; Increment (ref x); // dx takes the default value of 1 Increment (ref x, 2); // dx takes the value 2 In addition, to complement optional parameters, it is possible to explicitly specify parameter names in method calls, allowing to selectively pass any given subset of optional ...
a == b and b == c, but a != c), or make certain values be equal to their own negation. [2] A strict equality operator is also often available in those languages, returning true only for values with identical or equivalent types (in PHP, 4 === "4" is false although 4 == "4" is true).
Undefined parameter values are tricky: if the first positional parameter was not defined in the template call, then {{{1}}} will evaluate to the literal string "{{{1}}}" (i.e., the 7-character string containing three sets of curly braces around the number 1), which is a true value.
Shell variables, created using the set or @ statements, are internal to C shell. They are not passed to child processes. Shell variables can be either simple strings or arrays of strings. Some of the shell variables are predefined and used to control various internal C shell options, e.g., what should happen if a wildcard fails to match anything.