Foo.php

<?php
class Foo
{
    const BAR_ONE = 1;
    const BAR_TWO = 2;
    const BAR_THREE = 3;

    const QUX_1 = 'one';
    const QUX_2 = 'two';
    const QUX_3 = 'three';
    const QUX_CAKE = 'four';
}

$reflection = new \ReflectionClass(Foo::class);
echo $reflection->getConstants('BAR_'); // will return [1, 2, 3];