Download the PHP package mrsuh/php-generics without Composer

PHP generics written in PHP

Table of contents

• How it works
• Installation
• Monomorphization
• Type erasure
• Features
• Tests

How it works

In a nutshell:

• parse generics classes;
• generate concrete classes based on them (you can choose monomorphization or type-erasure);
• autoload concrete classes instead of generics classes.

For example, you need to add several PHP files:

• generic class Box;
• class Usage for use generic class;
• script with composer autoload and Usage class.

src/Box.php

src/Usage.php

bin/test.php

Generate concrete classes from generic classes with composer dump-generics command

What the composer dump-generics command does?

• finds all generic uses in classes (src/Usage.php for example).
• generates concrete classes from generic classes with unique names based on name and arguments of generic class.
• replaces generic class names to concrete class names in places of use.

In this case should be generated:

• 2 concrete classes of generics BoxForInt and BoxForString;
• 1 concrete class Usage with replaced generics class names to concrete class names.

Generate vendor/autoload.php with composer dump-autoload command

Run bin/test.php script

Composer autoload first checks the "cache" directory and then the "src" directory to load the classes.

:blue_book: You can find repository with this example here.

Installation

Require

• PHP >= 7.4
• Composer (PSR-4 Autoload)

Install library

Add directory("cache/") to composer autoload PSR-4 for generated classes. It should be placed before the main directory.

composer.json

Monomorphization

A new class is generated for each generic argument combination.

Before monomorphization:

After monomorphization:

Command

Where in class can generics be used?

Where in generic class can parameters be used?

:blue_book: You can read more about monomorphization here.

Type erasure

A new class is generated without generics arguments.

Before type erasure:

After type erasure:

Command

Where in class can generics be used?

Where in generic class can parameters be used?

:blue_book: You can read more about type-erasure here.

Features

What syntax is used?

The RFC does not define a specific syntax so i took this one implemented by Nikita Popov

Syntax example:

Syntax problems

I had to upgrade nikic/php-parser for parse code with new syntax.
You can see here the grammar changes that had to be made for support generics.

Parser use PHP implementation of YACC.
The YACC(LALR) algorithm and current PHP syntax make it impossible to describe the full syntax of generics due to collisions.

Collision example:

Solution options

Therefore, nested generics are not currently supported.

Parameter names have not special restrictions

Several generic parameters support

Default generic parameter support

How fast is it?

All concrete classes are pre-generated and can be cached(should not affect performance).

Generating many concrete classes should negatively impact performance when:

• resolves concrete classes;
• storing concrete classes in memory;
• type checking for each concrete class.

I think it's all individual for a specific case.

Doesn't work without composer autoload

Autoload magic of concrete classes works with composer autoload only.
Nothing will work because of syntax error if you include file by "require"

Reflection

PHP does type checks in runtime.
Therefore, all generics arguments must me available through reflection in runtime.
It can't be, because information about generics arguments is erased after concrete classes are generated.

Tests

How to run tests?

How to add test?

• Add directory 00-your-dir-name to ./tests/{monomorphic/type-erased}
• Generate output files and check it