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Partials: Compile-time metaprogramming

For situations where more logic than just "compiler-assisted copy&paste" using PHP's traits is necessary, this library provides a syntax that expand dynamically based on the containing class at compile time.

Partial flavors

The partials provided by this library's are divided in two flavors: Kinds and composeables.

• Kinds define the general concept of a type. You can say, e.g.: This type is a list of something, or a reference to something. Or, to use more concrete examples: The Customers class is a list of customers (encapsulated by Customer instances), and Name is a reference to (a string) containing a name.
• Composeables can be used alone or in combination to extend a base type or a kind. You can say, e.g. This type comes with a certain functionality. Again, using a realistic use-case: The Person class comes with toString(), compareTo() and hashCode() methods.

Regardless of their flavor, some partials are actually implemented by a regular PHP trait, others are dynamically created at runtime. However, the syntax for both is use [Containing-Type]\[is-or-with]\[Partial-Name].

Walk-through

The Box trait creates a value object wrapping around exactly one member. It creates a one-arg constructor, and a value() for retrieving the value, and includes appropriate hashCode(), compareTo() and toString() implementations.

Writing this:

...is equivalent to:

The parametrized Accessors trait creates accessors for all instance members.

Writing this:

...is equivalent to:

If the constructor consists solely of assignments, you can include the Constructor trait and remove it. The parameters will be declared in the order the fields are declared: top to bottom, left to right in the source code.

Writing this:

...is equivalent to:

To combine all these, you can use the Value trait, which a) creates a constructor with all members as parameters, b) accessors for reading these, and c) implements the hashCode(), compareTo() and toString() methods.

The ListOf trait creates a list of elements which can be accessed by their offset, iterated by foreach, and offers equals() and toString() default implementations.

Writing this:

...is equivalent to:

The Builder trait will add a static with() method to your class, generating a fluent interface to create instances. This is especially useful in situation where there are a lot of constructor parameters.

The Comparators trait adds static by[Member] methods returning util.Comparator instances for each member. These instances can be combined using then (Post::byDate()->then(Post::byAuthor())) or reversed (Post::byDate()->reverse()).

The ListIndexedBy trait creates a list of elements which can be queried by name, also overloading iteration and creating equals() and toString() in a sensible manner. The class needs to implement the abstract index method and return a string representing the name.

Putting it all together, we can see the API:

See also

• http://groovy-lang.org/metaprogramming.html
• http://projectlombok.org/