View file vendor/laravel/framework/src/Illuminate/Routing/CreatesRegularExpressionRouteConstraints.php

<?php

namespace Illuminate\Routing;

use Illuminate\Support\Arr;

trait CreatesRegularExpressionRouteConstraints
{
    /**
     * Specify that the given route parameters must be alphabetic.
     *
     * @param  array|string  $parameters
     * @return $this
     */
    public function whereAlpha($parameters)
    {
        return $this->assignExpressionToParameters($parameters, '[a-zA-Z]+');
    }

    /**
     * Specify that the given route parameters must be alphanumeric.
     *
     * @param  array|string  $parameters
     * @return $this
     */
    public function whereAlphaNumeric($parameters)
    {
        return $this->assignExpressionToParameters($parameters, '[a-zA-Z0-9]+');
    }

    /**
     * Specify that the given route parameters must be numeric.
     *
     * @param  array|string  $parameters
     * @return $this
     */
    public function whereNumber($parameters)
    {
        return $this->assignExpressionToParameters($parameters, '[0-9]+');
    }

    /**
     * Specify that the given route parameters must be UUIDs.
     *
     * @param  array|string  $parameters
     * @return $this
     */
    public function whereUuid($parameters)
    {
        return $this->assignExpressionToParameters($parameters, '[\da-fA-F]{8}-[\da-fA-F]{4}-[\da-fA-F]{4}-[\da-fA-F]{4}-[\da-fA-F]{12}');
    }

    /**
     * Apply the given regular expression to the given parameters.
     *
     * @param  array|string  $parameters
     * @param  string  $expression
     * @return $this
     */
    protected function assignExpressionToParameters($parameters, $expression)
    {
        return $this->where(collect(Arr::wrap($parameters))
                    ->mapWithKeys(function ($parameter) use ($expression) {
                        return [$parameter => $expression];
                    })->all());
    }
}