?? Null Coalescing Operator

Returns the right operand if the left operand is empty / undefined (expression)

Description

The Null Coalescing operator is a little like a conditional where the result of the operation is the first non-empty value from left to right.

An empty value is any of the following:

Other “falsy” values such as numerical values of 0, boolean false, zero length strings and strings containing "null" are not considered empty by the null coalescing operator.

Examples

Assign with a default value

» $foo = $bar ?? "baz"

If $bar is unset then the value of $foo will be “baz”.

Multiple operators

» $unset_variable ?? null ?? "foobar"
foobar

Detail

The following extract was taken from Wikipedia:

The null coalescing operator (called the Logical Defined-Or operator in Perl) is a binary operator that is part of the syntax for a basic conditional expression in several programming languages. While its behavior differs between implementations, the null coalescing operator generally returns the result of its left-most operand if it exists and is not null, and otherwise returns the right-most operand. This behavior allows a default value to be defined for cases where a more specific value is not available.

In contrast to the ternary conditional if operator used as x ? x : y, but like the binary Elvis operator used as x ?: y, the null coalescing operator is a binary operator and thus evaluates its operands at most once, which is significant if the evaluation of x has side-effects.

See Also


This document was generated from gen/expr/null-coalescing-op_doc.yaml.

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