UPDATE: I added this post to the new Haxe.org blog: http://haxe.org/blog/importhx-intro

Out of ton of improvements coming in Haxe 3.3 (that will be released quite soon), I'd like to write a small intro for a completely new feature: import.hx AKA defaults.

This feature allows us to define imports and usings that will be applied for all modules inside a directory, which is particularly handy for large code bases with a lot of helpers and static extensions.

Imagine we have some DataTypes module containing types common to the whole project:

DataTypes.hx

typedef Person = {
    var name:String;
    var age:Int;
}

typedef Company = {
    var name:String;
    var employees:Array<Person>;
}

Then we also have Logger module containing static logging function that we also want to use across our project:

Logger.hx

class Logger {
    public static function log(msg:String):Void { /* ... */ }
    public static function warn(msg:String):Void { /* ... */ }
}

And finally, we have some handy static extensions in the Tools module:

Tools.hx

class Tools {
    public static function hasEmployee(company:Company, person:Person) {
        return company.employees.indexOf(person) != -1;
    }
}

To use all these in a module with our actual logic, we'd have to add imports and usings to our module, like this:

import Logger.*; // import all statics from the Logger class
import DataTypes; // import types from the DataTypes module
using Tools; // enable static extensions from the Tools class

That is 3 lines that you have to add in all your modules which can become quite annoying when you have a lot of them. Thankfully, with a new import.hx feature, you can create a special import.hx file (note the lowercase name!) in the directory where your code lies, place those imports in that file, and they will be applied to all haxe modules in this directory and its subdirectories.

So, if we move those imports in the import.hx file, then we can write our code without import/using directives and still have them applied, e.g.

Main.hx

// look, no import or using directives!

class Main {
    static function main() {
        // use a static method from the Logger class
        log("Hello");

        // use Person type from the DataTypes module
        var sarah:Person = {name: "Sarah", age: 23}; 
        var john:Person = {name: "John", age: 38};

        // use Company type from the DataTypes module
        var company:Company = {
            name: "Bricks & Blocks",
            employees: [john, sarah]
        };

        // use `hasEmployee` extension method from the Tools class
        var johnIsEmployee = company.hasEmployee(john);

        // user another static method from the Logger class
        warn('John is employee: $johnIsEmployee');
    }
}

Cool, right? :)