How to Inline Value Object in Symfony PHP Config

Why are Value Objects in Configuration Priceless?

Let's say we want to rename dump() func call to Tracy\Debugger::dump().

-dump($value);
+Tracy\Debugger::dump($value);

KISS. Why not use a simple array?

Look at our previous post about why the road to hell is paved with good intentions.

Now that we know why and when we want to use value objects, the question is How can we use them in Symfony PHP Config?

1. Direct Object

First obvious idea is to just use is like we would in PHP:

// very dummy PHP approach
$funcCallToStaticCallRector = new FuncCallToStaticCallRector();

$configuration = [
    FuncCallToStaticCallRector::FUNC_CALLS_TO_STATIC_CALLS => [
         new FuncCallToStaticCall('dump', 'Tracy\Debugger', 'dump'),
    ]
];

$funcCallToStaticCallRector->configure($configuration);

This should work, right? It's just passing a bunch of scalar values:

// rector.php

$services->set(FuncCallToStaticCallRector::class)
    ->call('configure', [[
        FuncCallToStaticCallRector::FUNC_CALLS_TO_STATIC_CALLS => [
            new FuncCallToStaticCall('dump', 'Tracy\Debugger', 'dump'),
        ]
    ]]);

↓

 [ERROR] Cannot use values of type
         "Rector\Transform\ValueObject\FuncCallToStaticCall" in service
         configuration files.

2. Native inline_service() Function

Fortunately, Symfony gives us a little trick. The inline_service() basically registers a local service, just for the configuration:

// rector.php

$services->set(FuncCallToStaticCallRector::class)
    ->call('configure', [[
        FuncCallToStaticCallRector::FUNC_CALLS_TO_STATIC_CALLS => [
            inline_service(FuncCallToStaticCall::class)
                ->args(['dump', 'Tracy\Debugger', 'dump']),
        ]
    ]]);

This works!

There is just little detail. The IDE autocomplete we want from value objects:

...is gone.

• How can we know there are precisely 3 arguments?
• What is their order?
• What is their name?
• When does __construct() type validation happens?

This approach shuts us back to coding in the dark with Notepad.

3. Best of Both Worlds - inline_value_objects()

What we need here?

• A value object configuration that looks like a value object:

  new SomeClass('value');
  

• 1 line solution

• Ideally, in Symfony way, so it the least surprise to use

To cover all benefits together, we've created custom ValueObjectInliner class:

// rector.php
$services->set(FuncCallToStaticCallRector::class)
    ->call('configure', [[
        FuncCallToStaticCallRector::FUNC_CALLS_TO_STATIC_CALLS => ValueObjectInliner::inline([
            new FuncCallToStaticCall('dump', 'Tracy\Debugger', 'dump'),
            new FuncCallToStaticCall('d', 'Tracy\Debugger', 'dump'),
        ])
    ]]);

4. Simple configure() Method

Since Rector 0.12 you can use ->configure() method, that handles the complexity for you:

$services->set(FuncCallToStaticCallRector::class)
    ->configure([
        new FuncCallToStaticCall('dump', 'Tracy\Debugger', 'dump'),
        // it handles multiple items without duplicated call
        new FuncCallToStaticCall('d', 'Tracy\Debugger', 'dump'),
        new FuncCallToStaticCall('dd', 'Tracy\Debugger', 'dump'),
    ]);

Instead of complexity keys, constants and inliners, just pass it array of value objects.

And you're set!

This way, anyone can configure even the most complex Rector rules without ever looking inside the Rector rule and scan for configuration values.

And What Rector uses What Value Object?

In convention over configuration principle, all you need to know the rule name.

Could you guess the value object naming pattern?

• FuncCallToStaticCallRector (rule)
• FuncCallToStaticCall (value object)

That's it!

Happy and safe coding!