<?php

function isCallable($obj, $method)
{
    //$test1 = method_exists($obj, $method);
    //var_dump($test1);
    //TRUE

    //$test2 = is_callable([$obj, $method]);
    //var_dump($test2);
    //FALSE

    return (method_exists($obj, $method) && is_callable([$obj, $method]));
}

trait helper
{
    public function show()
    {
        echo "show!";

        if(isCallable($this, "afterShow"))
        {
            $this->afterShow();
        }

        //$this->afterShow();

    }
}

class my_class
{
    use helper;

    private function afterShow()
    {
        echo "...then this.";
    }
}

$objMyClass = new my_class();

$objMyClass->show();