<?php
$variavel = "valor";

// com switch
switch($variavel){

case "a": break;
case "b":break;
default :
}

// workaround 1

$functionStrategy = "func{$variavel}";

$retorno = (function_exists($functionStrategy))?$functionStrategy():defaultStrategy();



function a(){
// estrategia A
}
function b(){
//estrategia B
}


// workaround 2

function Strategy($functionStrategy, &$retvalue)
{
 include_once "{$functionStrategy}.php";

$retvalue = (function_exists($functionStrategy))?$functionStrategy():defaultStrategy();

}



Strategy($variavel, $retorno);