HH\Lib\C\onlyx
Returns the first and only element of the given Traversable, or throws if the Traversable is empty or contains more than one element
namespace HH\Lib\C;
function onlyx<T>(
Traversable<T> $traversable,
?\HH\Lib\Str\SprintfFormatString $format_string = NULL,
mixed ...$format_args,
): T;
An optional format string (and format arguments) may be passed to specify a custom message for the exception in the error case.
For Traversables with more than one element, see C\firstx.
Time complexity: O(1) Space complexity: O(1)
Parameters
Traversable<T>$traversable?\HH\Lib\Str\SprintfFormatString $format_string = NULLmixed ...$format_args
Returns
T
Examples
$string = vec["a"];
$onlyx_result_1 = C\onlyx($string);
echo "First onlyx result: $onlyx_result_1\n";
//Output: First onlyx result: a
$strings = vec["a", "b"];
$onlyx_result_2 = C\onlyx($strings);
//Output: Hit a php exception : exception 'InvariantViolationException' with message
//'Expected exactly one element but got 2.'
$empty_strings = vec[];
$onlyx_result_3 = C\onlyx($empty_strings);
//Output: Hit a php exception : exception 'InvariantViolationException' with message
//'Expected non-empty Traversable.'