What I learn today

Contains my daily learning that I want to share with you😃

Flutter code compilation

Develop

(1) JIT + VM (Mobile & Desktop)

• JIT compiler converts program source code into native machine code just before program execution.
• “Just-in-Time” means making “only what is needed, when it is needed, and in the amount needed.”
• The file generated by JIT needs VM to run

(2) dartdevc (Web)

• Dart code transpiled into js code

DEPLOY

(1) AOT + runtime (Mobile & Desktop)

• The AOT compiler works by compiling your code before it is “delivered” to whatever runtime environment runs the code. To generate AOT snapshot

  dart2native bin/main.dart -k aot

• AOT generates single binary file that can run natively

(2) dart2js (Web)

Flutter working

• Platform exposes OEM (Original Equipment Manufacturer) widgets and service APIs for example camera to build UI and communicate platform services respectively.
• In cross platform world, OEM widgets and platform specific APIs can't be used directly because they are coming from different environment. For example, a Kotlin's android app is compiled to work with ART (Android Run Time) ecosystem. So, obviously it can't run on iOS which has no ART.
• React Native uses OEM widgets but solves the aforementioned problem using bridge (an abstraction layer) so that a developer does not need to be concerned about platform.
• Flutter uses completely different approach and uses Skia rendering engine to paint the UI so that OEM widgets are not needed anymore.
• Minimal Flutter app
  • Android: ~4.4 MB
  • iOS: ~10.9 MB

Constructors in Dart

• Named

Fraction.zero() : _numerator = 0, _denominator = 1;

• Redirecting

Fraction.oneHalf() : this(1,2);

• Factory

  • Returns an object not necessarily a new one
  • Cases where it is very useful:
    • To return an instance of subclass
    • To follow Singleton pattern
    • To return an instance from cache

• Const

  • When all class variables are final
  • It can be used as an annotation

  • class Todo{
      final int title;
      final int description;
      const A(this.title, this.description)
    }
    
    @Todo('Chibi', 'Rename class')
    class MyClass {
      @Todo('Tuwaise', 'Change fielld type')
      int value;
    
      @Todo('Anyone', 'Change format')
      void printValue() {
      	print('value: $value');
      }
    
      @Todo('Anyone', 'Remove this')
      MyClass();
    }
    
    void main() {
      MyClass myClass = new MyClass();
      InstanceMirror im = reflect(myClass);
      ClassMirror classMirror = im.type;
    
      classMirror.metadata.forEach((metadata) {
      	   if (metadata.reflectee is Todo) {
    		      print(metadata.reflectee.name);
    		      print(metadata.reflectee.description);
      	   }
      });
    
      for (var v in classMirror.declarations.values) {
      	   if (!v.metadata.isEmpty) {
    		      if (v.metadata.first.reflectee is Todo) {
      	         print(v.metadata.first.reflectee.name);
               print(v.metadata.first.reflectee.description);
    		      }
                 }
          }
     }