I've got a rendering engine, much like React where I need to store classes rather than instances in an object for compiling.
So for example, I have a Button component that I would like to be able to dynamically instantiate. Doing this would be as easy as
new components["Button"]
For this, I need a list of all possible classes. So I've got a Dictionary interface declared like so:
interface Dictionary<T> {
[Key: string]: T;
}
This works well, I'm easily able to add objects to this dictionary. Except if I have an object:
const components: Dictionary<Component> = {
Button: Button
}
Then I get an error because Button is a class, rather than an instance. Here, the issue is, I don't want to define the dictionary as Dictionary<Function> because that would mean I allow any function into the dictionary. Specifically, I only want to allow classes into the dictionary that extend the Component class.
How would I achieve this?
You also need to define the signature of the constructor (which makes sense if you think about it), but you do the following:
interface ComponentClass {
new (a: number): Component;
}
(The signature of the constructor is probably not "number", but put in whatever it is.)
Related
I have the follwoing code from tutorial|:
constructor(#InjectModel('User') private readonly userModel: Model<User>) {}
Where User is:
export interface User extends Document {
readonly name: string;
readonly age: number;
readonly phone: string;
}
Could you explain how #InjectModel works, what is 'User' and why we passed Model<User>, what does it mean?
What I can inject also using #InjectModel?
All right, to get into this, first we have to take to truth that interfaces do not exist at runtime. So the User interface you have is only useful during development. I'll try to break this down step by step, starting from the end of the line and working backwards.
Model<User>: Model is an interface type exposed by mongoose that allows us to know that the model we're using has methods like find and create. By saying Model<User> we are saying "This is a mongoose model object that refers to the User interface. This is especially useful for Typescript because as the functions are typed with generics, it knows what the return of methods like find are: an array of User objects. The model interface is really Model<T> where T is the interface that extends Document (another mongoose type).
What is 'User': 'User' is the string equivalent of the name of the interface. If your interface that extends Document is called Dog you use 'Dog', if it's Animal you use 'Animal'. The reason for not passing the interface is because interfaces do not exist at runtime (unlike classes).
How does #InjectModel() work: Okay, the really fun part of the question to answer. Nest works normally by using Injection Tokens. Normally, these tokens are determined by the type of the injected value. In your case Model<User>. Now, the problem here is that A) interfaces don't exist at runtime and B) Typescript does not reflect generics well, so even if Model was a class, all that could be gotten would be Model which isn't enough information on what to inject. So the next logical step Nest takes is to allow a user to provide injection tokens and use the #Inject() decorator. You can do things like injecting an object this way (like package configuration information). Useful, but a bit hard to work with without building your own providers. Now steps in #InjectModel(). #InjectModel() builds an injection token based on the string that's passed into the function. This token is something along the lines of typeModel where type is actually what you pass into the function. This tells Nest specifically what model we are injecting. This also needs to align with the provider created with MongooseModule.forFeature(), hence why name and the value passed to #InjectModel() need to be aligned. Usually it's easiest to align when they use the same string name as the interface.
I'm doing this Ensime package for Atom.io https://github.com/ensime/ensime-atom and I've been thinking about the possibility to use scala.js instead of writing Coffeescript.
Atom is a web based editor which is scripted with js and is node.js based. A plugin/package defines it's main entry point by pointing out a javascript object with a few specific.
I figured I should start out simple and try using scala.js replacing the simplest coffeescript file I have:
{View} = require 'atom-space-pen-views'
# View for the little status messages down there where messages from Ensime server can be shown
module.exports =
class StatusbarView extends View
#content: ->
#div class: 'ensime-status inline-block'
initialize: ->
serialize: ->
init: ->
#attach()
attach: =>
statusbar = document.querySelector('status-bar')
statusbar?.addLeftTile {item: this}
setText: (text) =>
#text("Ensime: #{text}").show()
destroy: ->
#detach()
As you can see this exports a require.js module and is a class extending a class fetched with require as well.
Sooo.
I'm thinking I'd just use Dynamic for the require dep as I've seen on SO How to invoke nodejs modules from scala.js?:
import js.Dynamic.{global => g}
import js.DynamicImplicits._
private[views] object SpacePen {
private val spacePenViews = require("atom-space-pen-views")
val view = spacePenViews.view
}
But if I wanted to type the super-class, could I just make a facade-trait and do asInstanceOf?
Secondly, I wonder how I can export my class as a node module. I found this:
https://github.com/rockymadden/scala-node/blob/master/main/src/main/coffeescript/example.coffee
Is this the right way? Do I need to do the sandboxing? Couldn't I just get moduleimported from global and write module.exports = _some_scala_object_?
I'm also wondering how I could extend existing js classes. The same problem as asked here, but I don't really understand the answer:
https://groups.google.com/forum/#!topic/scala-js/l0gSOSiqubs
My code so far:
private[views] object SpacePen {
private val spacePenViews = js.Dynamic.global.require("atom-space-pen-views")
type View = spacePenViews.view
}
class StatusBarView extends SpacePen.View {
override def content =
super.div()
}
gives me compile errors that I can't extend sealed trait Dynamic. Of course.
Any pointers highly appreciated!
I'm not particularly expert in Node per se, but to answer your first question, yes -- if you have a pointer to a JS object, and you know the details of its type, you can pretty much always define a facade trait and asInstanceOf to use it. That ought to work.
As for the last bit, you basically can't extend JS classes in Scala.js -- it just doesn't work. The way most of us get around that is by defining implicit classes, or using implicit def's, to get the appearance of extending without actually doing so.
For example, given JS class Foo, I can write
implicit class RichFoo(foo:Foo) {
def method1() = { ... }
}
This is actually a wrapper around Foo, but calling code can simply call foo.method1() without worrying about that detail.
You can see this approach in action very heavily in jquery-facade, particularly in the relationship between JQuery (the pure facade), JQueryTyped (some tweaked methods over JQuery to make them work better in Scala), and JQueryExtensions (some higher-level functions built around JQuery). These are held together using implicit def's in package.scala. As far as calling code is concerned, all of these simply look like methods on JQuery.
I have an annotation which adds some methods and default constructor to annotated class.
I have managed to create a gdsl, to enable autocompletion in idea for methods, but I'm stuck with constructor and documentation is very poor.
Does anyone have any ideas, how to do this?
Maybe I could find a solution, in existing gdsl, but I can't remember any Transformation, related to constructors. Maybe you can remind me of any of them.
def objectContext = context(ctype: "java.lang.Object")
contributor(objectContext) {
if (hasAnnotation("com.xseagullx.SomeAnnotation")) {
// Here I want to add constructor's declaration(with empty arg's)
// …
// And then my methods.
method name: 'someMethod', type: 'void', params: [:]
}
}
EDITED: OK, if it's as #jasp say, and there is no DSL construct for declaring Constructors, I'm still asking for a good documentation sources, other than JB's confluence page. Tutorials and other sources. I'm familiar with embedded dsl's for groovy, grails and gradle.
Need smth. more structured, if it's possible.
All function invocations inside of GroovyDSL are just calls to wrappers around internal IDEA's Program Structure Interface (PCI). However it doesn't cover all of PCI's abilities, including default constructors functionality I believe. One of an evidence for that is singletonTransform.gdsl, which is bundled into IDEA from 9 version and describes #Singleton AST transformation. Here is it's code:
contributor(context()) {
if (classType?.hasAnnotation("groovy.lang.Singleton")) {
property name: "instance",
type: classType?.getQualifiedName() ?: "java.lang.Object",
isStatic: true
}
}
As you can see it doesn't change a constructor and it's visibility, so IDEA will autocomplete this invalid code:
#Singleton class Foo {}
def foo = new Foo()
Futhermore GDSL that describes the semantics of GroovyDSL (which is actually the part of /plugins/groovy/resources/standardDsls/metaDsl.gdsl of IDEA sources) doesn't provide any ability for describing of constructors.
In this case I suggest you use newify transformation which allows you to describe targetClass.name method returning created instance.
I know this is a bit old, but I found myself looking for something similar.
The DSL you are looking for is
method params: [:], constructor: true although I don't understand why you'd need it; if a class doesn't declare any constructors doesn't IDEA always suggest the default one?
I am trying to save an Object which implements an Interface say IInterface.
private PersistentDictionary<string, IInterface> Object = new PersistentDictionary<string, IInterface>(Environment.CurrentDirectory + #"\Object");
Since many classes implement the same interface(all of which need to cached), for a generic approach I want to store an Object of type IInterface in the dictionary.
So that anywhere I can pull out that object type cast it as IInterface and use that object's internal implementation of methods etc..
But, as soon as the Esent cache is initialized it throws this error:
Not supported for SetColumn
Parameter name: TColumn
Actual value was IInterface.
I have tried to not use XmlSerializer to do the same but is unable to deserialize an Interface type.Also, [Serializable] attribute cannot be used on top of a Interface, so I am stuck.
I have also tried to make all the implementations(classes) of the Interface as [Serializable] as a dying attempt but to no use.
Does any one know a way out ? Thanks in advance !!!
The only reason that only structs are supported (as well as some basic immutable classes such as string) is that the PersistentDictionary is meant to be a drop-in replacement for Dictionary, SortedDictionary and other similar classes.
Suppose I have the following code:
class MyClass
{
int val;
}
.
.
.
var dict = new Dictionary<int,MyClass>();
var x = new MyClass();
x.val = 1;
dict.Add(0,x);
x.val = 2;
var y = dict[0];
Console.WriteLine(y.val);
The output in this case would be 2. But if I'd used the PersistentDictionary instead of the regular one, the output would be 1. The class was created with value 1, and then changed after it was added to the dictionary. Since a class is a reference type, when we retrieve the item from the dictionary, we will also have the changed data.
Since the PersistentDictionary writes the data to disk, it cannot really handle reference types this way. Serializing it, and writing it to disk is essentially the same as treating the object as a value type (an entire copy is made).
Because it's intended to be used instead of the standard dictionaries, and the fact that it cannot handle reference types with complete transparency, the developers instead opted to support only structs, because structs are value types already.
However, if you're aware of this limitation and promise to be careful not to fall into this trap, you can allow it to serialize classes quite easily. Just download the source code and compile your own version of the EsentCollections library. The only change you need to make to it is to change this line:
if (!(type.IsValueType && type.IsSerializable))
to this:
if (!type.IsSerializable)
This will allow classes to be written to the PersistentDictionary as well, provided that it's Serializable, and its members are Serializable as well. A huge benefit is that it will also allow you to store arrays in there this way. All you have to keep in mind is that it's not a real dictionary, therefore when you write an object to it, it will store a copy of the object. Therefore, updating any of your object's members after adding them to the PersistentDictionary will not update the copy in the dictionary automatically as well, you'd need to remember to update it manually.
PersistentDictionary can only store value-structs and a very limited subset of classes (string, Uri, IPAddress). Take a look at ColumnConverter.cs, at private static bool IsSerializable(Type type) for the full restrictions. You'd be hitting the typeinfo.IsValueType() restriction.
By the way, you can also try posting questions about PersistentDictionary at http://managedesent.codeplex.com/discussions .
-martin
(this is a generalized example)
I'd like to create a utility method that can be called on any object, it'll have a signature like:
class StringMetaData {
Object value
String meta
}
Object.metaClass.withStringMetaData = { meta ->
new StringMetaData(delegate, meta)
}
With the idea that then anywhere in my program I could do something like:
def foo = 1.withStringMetaData("bar")
And now I can grab foo.value for the value or foo.meta for the attached String.
Within a local context, I'm able to define this meta method on Object, but I'd like to make it available globally within my application, what's the right way to make this metamethod available everywhere?
Perhaps a groovy extension module could help you. I never tried it myself, but the documentation states, that you can add custom methods to JDK classes.