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dartdart-mirrors
Faris Nasution
Faris Nasution

Reputation: 3620

Dart when to use the mirror API

This may be a silly question, so sorry for asking this, and fyi I'm new to this kind of stuff.

After reading the documentation about mirrors, I can only grasp that the mirrors API is just like copying some instance plus access to some method that I don't know when/why to use.

Anybody care to give me some pointers, some example would be nice.

Upvotes: 0

Views: 266

Answers (1)

Zdeslav Vojkovic
Zdeslav Vojkovic

Reputation: 14591

Mirror API allows you to retrieve metadata about objects and types programmatically (during execution) and to execute methods on objects . It is similar to reflection in .NET or Java.

A typical example is implementing plugin support:

Let's say that you define an IPlugin interface and want to automatically register with your PluginManager an instance of each type that implements it, without need to explicitly register each new implementation. Sometimes you even don't know all the plugins in advance, e.g. if users can deploy their own plugins.

You could do it like this (WARNING: I have never used Mirror API, so this is a high level description based on API documentation, not a proper implementation):

  • You first use MirrorSystem.libraries to get LibraryMirror instance for each library in that MirrorSystem
  • Then for each LibraryMirror you use classes property to get ClassMirror for each class in the library
  • For each ClassMirror use superinterfaces to get all implemented interfaces
  • If any of the implemented interfaces is IPlugin you can create an instance of that class (ClassMirror.newInstance) and register it with plugin manager.

Without mirror API, you would not be able to enumerate all the types, find what interfaces they implement (without creating an object) or create an instance of a type that you don't know about in advance.

To be honest I am not sure what is the current state of mirror API in Dart, I believe that it is still not finished, but I might be wrong.

Upvotes: 4

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