Creating Macros

[Dinko Pavicic]

Hi all,

I'm trying to fiddle with macros to build Maps filled with asset data but I totally suck at it.

I have a JSON with asset data grouped by the locale and also by the build target ( within the each locale ), something like this:

assets: {

  en: {

    html: [

      {

         name: "textureA",

         type: "texture",

         resource: "some_url_to_a_texture.png"

         isLoaded: false

      },

      {

         name: "meshA",

         type: "mesh",

         resource: "some_url_to_a_texture.fbx"

         isLoaded: false

      }

    ],

    ios: [

      {

         name: "textureA",

         type: "texture",

         resource: "some_url_to_a_texture_ios.png"

         isLoaded: false

      },

      {

         name: "meshA",

         type: "mesh",

         resource: "some_url_to_a_texture_ios.fbx"

         isLoaded: false

      }

    ],

    android: [

      {

         name: "textureA",

         type: "texture",

         resource: "some_url_to_a_texture_android.png"

         isLoaded: false

      },

      {

         name: "meshA",

         type: "mesh",

         resource: "some_url_to_a_texture_android.fbx"

         isLoaded: false

      }

    ]

  },

  fr: {

    html: [

      {

         name: "textureA",

         type: "texture",

         resource: "some_url_to_a_texture.png"

         isLoaded: false

      },

      {

         name: "meshA",

         type: "mesh",

         resource: "some_url_to_a_texture.fbx"

         isLoaded: false

      }

    ],

    ios: [

      {

         name: "textureA",

         type: "texture",

         resource: "some_url_to_a_texture_ios.png"

         isLoaded: false

      },

      {

         name: "meshA",

         type: "mesh",

         resource: "some_url_to_a_texture_ios.fbx"

         isLoaded: false

      }

    ],

    android: [

      {

         name: "textureA",

         type: "texture",

         resource: "some_url_to_a_texture_android.png"

         isLoaded: false

      },

      {

         name: "meshA",

         type: "mesh",

         resource: "some_url_to_a_texture_android.fbx"

         isLoaded: false

      }

    ]

  }

}

I have a class like this where I would like to create and populate Map(s) with asset data via macros

class AssetService

{

    /** Map with structure something like this:

     [ localeName =>  [

       assetName => asset, 

       assetName => asset,

       assetName => asset,

       ],

       localeName =>  [

       assetName => asset, 

       assetName => asset,

       assetName => asset,

       ]

     ]

    */

    private var _assets:Map<String, Map<String, Asset>>;

}

And a class for the assets, something like this

class Asset

{

  public var name:String;

  public var locale:String;

  public var resource:String;

  public var type:String;

}

My macro starts something like this ... It successfully load that json and parses it into an object but I really don't know how to create Maps with macros and set them to appropriate fields:

#if macro

class AssetMetadataBuilder

{

macro public static function build()

{

trace( "------- ASSET COMPILER ------- " );

trace("");

switch ( Context.getType("test.AssetService" ))

{

case TInst(cl,_):

var cl = cl.get();

var meta = cl.meta;

// Get assets config ... loads the assets.json file and parses it

var assetsData = AssetMetadataBuilder.loadAssetConfig();

                                

                               

                                ..... need to create and populate Maps with macros here ... I'm a dumbass

I tried to find similar stuff on the group but didn't have any luck. If anybody have any pointers about this I would be really grateful.

Many thanks in advance!

Dinko

[Dinko Pavicic]

I messed up the post subject, it should be 'creating Maps with macros'. 

Sorry for that

[Yoni Gueta]

i think this can do what your'e looking for:

https://github.com/jasononeil/compiletime

in your example, just replace your classes with typedefs and feed it to CompileTime.parseJsonFile("myJson.json")

[Dinko Pavicic]

Thanks, not exactly what I'm looking for but it's nice for macro learning purposes.

[Domagoj Štrekelj]

Hello,

I recently attempted something similar myself, though not with maps. There were some pitfalls, but nothing I couldn't overcome with some help from the good people frequenting the Haxe IRC channel.

What follows is a brief explanation of Haxe macro programming as I understand it. Feel free to move straight on to the code sample if you're not new to macros!

Haxe macros are an interesting exercise in meta-programming. We have been conditioned to write code to solve a problem; much like we are conditioned to "solve for X" in algebra by any means we see fit. Writing macros, however, puts the code into focus - we write code to reduce the number of steps required to reach a solution. These steps are expressions or Haxe source code, in simple terms.

Let's take for example your issue of outfitting an existing class with a variable of the map type. We know the data we want the map to store, and more importantly we know how to declare and initialize maps. Here is a simple map with Int keys mapped to String values:

var myMap : Map<Int, String> = [ 1 => "One", 2 => "Two", 3 => "Three" ];

We can see a pattern: key => value. And patterns are great for us programmers. We can exploit them to write less code, which is literally what happens when writing a macro.

Each one of those patterns is an expression, which means that the map is essentially an array of expressions. So here is what we need to do (in "pseudocode"):

myMap : Array<Expression> = [];

for (pair in dataset)
{
    myMap.push(pair.key => pair.value);
}

Here is where it gets tricky because now we actually have to write a macro. For the sake of brevity I won't go into detail and let the actual asset loading macro do the talking.

package;

import haxe.macro.Context;

import haxe.macro.Expr;

import haxe.macro.Type;

using haxe.macro.Tools;

class AssetServiceBuilder

{

    public static macro function build() : Array<Field>

    {

        // The build fields of the class being built

        var fields = Context.getBuildFields();

        // The asset data we want to store into a map

        var assetData : AssetData = haxe.Json.parse(sys.io.File.getContent("res/assets.json"));

        // The array of expressions representing the final map of assets

        var assets = [];

        

        // We use reflection to iterate through fields of the anonymous object that is assetData

        for (locale in Reflect.fields(assetData))

        {

            // This is akin to assetData[locale] or assetData.locale

            var l : AssetData.AssetLocaleData = Reflect.field(assetData, locale);

            // The array of expressions representing the internal map of assets per platform

            var localAssets = [];

            

            for (platform in Reflect.fields(l))

            {

                var p : AssetData.AssetPlatformData = Reflect.field(l, platform);

                // I'm only looking at the assets for a single platform to avoid duplicate keys

                if (platform == "ios")

                {

                    for (entry in p)

                    {

                        // Note the use of `macro` and expression reification (`$v{}`)

                        localAssets.push(macro $v{entry.name} => new Asset($v{locale}, $v{entry.name}, $v{entry.resource}, $v{entry.type}));

                    }

                }

            }

            // Note the use of `macro` and expression reification (`$a{}`)

            assets.push(macro $v{locale} => $a{localAssets});

        }

        

        // We "push" (add) a new field to the class

        fields.push({

            // Think of this as the line position that will be referenced on error

            pos: Context.currentPos(),

            // Field name

            name: "_assets",

            // We won't be adding any metadata

            meta: null,

            // The field will be a variable of the Map<String, Map<String, Asset>> type, and will contain the array of expressions making up a map

            kind: FieldType.FVar(macro : Map<String, Map<String, Asset>>, macro $a{assets}),

            // We won't be adding any documentation

            doc: null,

            // We'll give it private visibility

            access: [Access.APrivate]

        });

        

        // Once the build macro is done it needs to return the context's build fields

        return fields;

    }

}

Here is a comprehensive gist.

I would recommend building with -D dump=pretty when writing macros because the AST-like dump of the macro result is enlightening. In this case, it looks kind of like this:

class AssetService{

private _assets(var) : Map<String, Map<String, Asset>>

= {

var _g = new haxe.ds.StringMap();

{

var value;

{

var _g1 = new haxe.ds.StringMap();

{

var value1 = new Asset("en","textureA","some_url_to_a_texture_ios.png","texture");

__dollar__hset(_g1.h,"textureA".__s,value1,null);

};

{

var value1 = new Asset("en","meshA","some_url_to_a_texture_ios.fbx","mesh");

__dollar__hset(_g1.h,"meshA".__s,value1,null);

};

value = _g1;

};

__dollar__hset(_g.h,"en".__s,value,null);

};

{

var value;

{

var _g2 = new haxe.ds.StringMap();

{

var value1 = new Asset("fr","textureA","some_url_to_a_texture_ios.png","texture");

__dollar__hset(_g2.h,"textureA".__s,value1,null);

};

{

var value1 = new Asset("fr","meshA","some_url_to_a_texture_ios.fbx","mesh");

__dollar__hset(_g2.h,"meshA".__s,value1,null);

};

value = _g2;

};

__dollar__hset(_g.h,"fr".__s,value,null);

};

_g;

}

}

I hope this was helpful!

Domagoj

P.S.

Pozdrav iz Osijeka :) Ako želiš s nekim "lokalnim" razgovarati o Haxeu, slobodno mi se javi!

[Dinko Pavicic]

Wow!

I don't know how to thank you for putting so much effort in this explanation! Many thanks, this really helps !!!

Nice to see that there's Haxers in Croatia.

Take care,

Dinko