IEnumerable.single() method

IEnumerable->single([$predicate]) method

Returns the one and only element of the sequence (s. Single()).

An exception is thrown, if more than one element was found or no element was found.

Syntax

public function single([ predciate $predicate = null ]]) : mixed;

Parameters

Name	Type	Description
$predicate	[[predicate	Predicate]]

$predicate

The custom predciate to use.

Result

The one and only value of the sequence.

Examples

Default

use \System\Collections\ElementNotFoundException;
use \System\Collections\EnumerableException;
use \System\Linq\Enumerable;

$seq1 = Enumerable::fromValues(11);
$seq2 = Enumerable::fromValues();
$seq3 = Enumerable::fromValues(1, 2);

// 11
$val1 = $seq1->single();

try {
    $val2 = $seq2->single();
}
catch (ElementNotFoundException $ex) {
    // code goes here
}

try {
    $val3 = $seq3->single();
}
catch (EnumerableException $ex) {
    // the code should be go here
    $thrownEx = $ex;
}

// (true)
$is1 = isset($thrownEx) && 
       ($thrownEx instanceof EnumerableException);
// (false)
$is2 = isset($val3);

Predicate (lambda)

use \System\Collections\ElementNotFoundException;
use \System\Collections\EnumerableException;
use \System\Linq\Enumerable;

$seq1 = Enumerable::fromValues(11);
$seq2 = Enumerable::fromValues(10, 11);
$seq3 = Enumerable::fromValues(9, 10, 11);

$predicate = '$x => $x < 11';

try {
    $val1 = $seq1->single($predicate);
}
catch (ElementNotFoundException $ex) {
    // code goes here
}

// 10
$val2 = $seq2->single($predicate);

try {
    $val3 = $seq3->single($predicate);
}
catch (EnumerableException $ex) {
    // the code should be go here
    $thrownEx = $ex;
}

// (true)
$is1 = isset($thrownEx) && 
       ($thrownEx instanceof EnumerableException);
// (false)
$is2 = isset($val3);

Predicate (closure)

use \System\Collections\ElementNotFoundException;
use \System\Collections\EnumerableException;
use \System\Linq\Enumerable;

$seq1 = Enumerable::fromValues(11);
$seq2 = Enumerable::fromValues(10, 11);
$seq3 = Enumerable::fromValues(9, 10, 11);

$predicate = function ($x) {
                 return $x < 11;
             };

try {
    $val1 = $seq1->single($predicate);
}
catch (ElementNotFoundException $ex) {
    // code goes here
}

// 10
$val2 = $seq2->single($predicate);

try {
    $val3 = $seq3->single($predicate);
}
catch (EnumerableException $ex) {
    // the code should be go here
    $thrownEx = $ex;
}

// (true)
$is1 = isset($thrownEx) && 
       ($thrownEx instanceof EnumerableException);
// (false)
$is2 = isset($val3);