Is there an equivalent of "let" vs. "var" in PHP? - php

Question

I have recently started with learning Swift for iOS development. I have a background in scripting languages, especially PHP. Seeing that it is emphasized using let to define a constant in favor of var to have the compiler optimize the resulting code, I wondered: is there an equivalent for PHP? Or does it simply not apply as PHP is not statically compiled?
I tried my luck at searching but found no satisfying information on that point.

Answer 1

No, you can't have locally scoped constants in PHP. All PHP constants are always globally visible. There is also no concept like immutable/mutable variables.
You can implement immutable object members (PHP: immutable public member fields), but it's a different thing.
Actually there is a const keyword in the language, but the docs say:
Note:
As opposed to defining constants using define(), constants defined using the const keyword must be declared at the top-level scope because they are defined at compile-time. This means that they cannot be declared inside functions, loops, if statements or try/ catch blocks.
(from http://php.net/manual/en/language.constants.syntax.php)
Interpreted languages with a dynamic type systems can have something like the swift let statement, so this is not because swift is compiled and PHP is interpreted (for example, there is a javascript proposal to introduce that feature: https://developer.mozilla.org/de/docs/Web/JavaScript/Reference/Statements/const)

Answer 2

Is there an equivalent of “let” vs. “var” in PHP?
PHP doesn't have let as a native language feature, yet (as of current version 7.1.4 - 04/2017)
But, some high-performance extensions like Phalcon and Ice have support for let, because of the underlying usage of zephir-lang.
So, there is let, but indirectly; using the above mentioned extensions.
There are two use cases:
define a variable from a super global
define a variable in the local PHP symbol table, e.g.
// set variable $price in PHP
let name = "price";
let {name} = 10.2;
As an example take a look at the source for the Ice Router:
namespace Ice\Mvc\Route;
use Ice\Mvc\Route\Parser\ParserInterface;
use Ice\Mvc\Route\DataGenerator\DataGeneratorInterface;
use Ice\Mvc\Route\Parser\Std;
use Ice\Mvc\Route\DataGenerator\GroupCount as Generator;
class Collector
{
private routeParser { set };
private dataGenerator { set };
/**
* Constructs a route collector.
*
* #param RouteParser $routeParser
* #param DataGenerator $dataGenerator
*/
public function __construct(<ParserInterface> routeParser = null, <DataGeneratorInterface> dataGenerator = null)
{
if !routeParser {
let routeParser = new Std();
}
if !dataGenerator {
let dataGenerator = new Generator();
}
let this->routeParser = routeParser,
this->dataGenerator = dataGenerator;
}
/**
* Adds a route to the collection.
*
* The syntax used in the $route string depends on the used route parser.
*
* #param string|array $httpMethod
* #param string $route
* #param mixed $handler
*/
public function addRoute(var httpMethod, string route, handler = null)
{
var routeDatas, routeData, method;
let routeDatas = this->routeParser->parse(route);
if typeof httpMethod == "string" {
let method = httpMethod,
httpMethod = [method];
}
for method in httpMethod {
for routeData in routeDatas {
this->dataGenerator->addRoute(method, routeData, handler);
}
}
}
/**
* Returns the collected route data, as provided by the data generator.
*
* #return array
*/
public function getData()
{
return this->dataGenerator->getData();
}
}