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    <h3>Editing: UnaryOperator.php</h3>
    <textarea name="content" rows="20" cols="80">&lt;?php declare(strict_types=1);
/*
 * This file is part of PHPUnit.
 *
 * (c) Sebastian Bergmann &lt;sebastian@phpunit.de&gt;
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */
namespace PHPUnit\Framework\Constraint;

use function count;

use SebastianBergmann\RecursionContext\InvalidArgumentException;

/**
 * @no-named-arguments Parameter names are not covered by the backward compatibility promise for PHPUnit
 */
abstract class UnaryOperator extends Operator
{
    /**
     * @var Constraint
     */
    private $constraint;

    /**
     * @param Constraint|mixed $constraint
     */
    public function __construct($constraint)
    {
        $this-&gt;constraint = $this-&gt;checkConstraint($constraint);
    }

    /**
     * Returns the number of operands (constraints).
     */
    public function arity(): int
    {
        return 1;
    }

    /**
     * Returns a string representation of the constraint.
     */
    public function toString(): string
    {
        $reduced = $this-&gt;reduce();

        if ($reduced !== $this) {
            return $reduced-&gt;toString();
        }

        $constraint = $this-&gt;constraint-&gt;reduce();

        if ($this-&gt;constraintNeedsParentheses($constraint)) {
            return $this-&gt;operator() . '( ' . $constraint-&gt;toString() . ' )';
        }

        $string = $constraint-&gt;toStringInContext($this, 0);

        if ($string === '') {
            return $this-&gt;transformString($constraint-&gt;toString());
        }

        return $string;
    }

    /**
     * Counts the number of constraint elements.
     */
    public function count(): int
    {
        return count($this-&gt;constraint);
    }

    /**
     * Returns the description of the failure.
     *
     * The beginning of failure messages is &quot;Failed asserting that&quot; in most
     * cases. This method should return the second part of that sentence.
     *
     * @param mixed $other evaluated value or object
     *
     * @throws InvalidArgumentException
     */
    protected function failureDescription($other): string
    {
        $reduced = $this-&gt;reduce();

        if ($reduced !== $this) {
            return $reduced-&gt;failureDescription($other);
        }

        $constraint = $this-&gt;constraint-&gt;reduce();

        if ($this-&gt;constraintNeedsParentheses($constraint)) {
            return $this-&gt;operator() . '( ' . $constraint-&gt;failureDescription($other) . ' )';
        }

        $string = $constraint-&gt;failureDescriptionInContext($this, 0, $other);

        if ($string === '') {
            return $this-&gt;transformString($constraint-&gt;failureDescription($other));
        }

        return $string;
    }

    /**
     * Transforms string returned by the memeber constraint's toString() or
     * failureDescription() such that it reflects constraint's participation in
     * this expression.
     *
     * The method may be overwritten in a subclass to apply default
     * transformation in case the operand constraint does not provide its own
     * custom strings via toStringInContext() or failureDescriptionInContext().
     *
     * @param string $string the string to be transformed
     */
    protected function transformString(string $string): string
    {
        return $string;
    }

    /**
     * Provides access to $this-&gt;constraint for subclasses.
     */
    final protected function constraint(): Constraint
    {
        return $this-&gt;constraint;
    }

    /**
     * Returns true if the $constraint needs to be wrapped with parentheses.
     */
    protected function constraintNeedsParentheses(Constraint $constraint): bool
    {
        $constraint = $constraint-&gt;reduce();

        return $constraint instanceof self || parent::constraintNeedsParentheses($constraint);
    }
}
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