Use of getter and Setter on Dart

Question

I can not understand the real need to use the Get/Set for the case below, which, even if I leave the variable commotion private, I could still modify it by using methods.

class casa {
  int comodos = 4;
}

void main() {
  casa casa1 = casa();
  casa1.comodos = 10;
  print(casa1.comodos);
}

Answer 1

Dear @Aiken, if you do by the methods you can modify by methods you can treat the input, allowing only "correct" values for the class rule/logic. This is the basics of "visibility" in OO with variables (read on the visibility of variables at the end of the answer, in case you don’t know how to use in Dart).

You is who will define what can and cannot, if it is public can "all" (in case any value int valid/acceptable). Now imagine your intention to comodos were a range limited from 5 to 50, anyone could put 4 or less, 51 or more, as values if it is "public", if private and treat by a method set of life then an IF will be more than enough to solve the limit range rule, example:

import 'dart:io';

class casa
{
  int _comodos = 4;

  setComodos(int value) {
    if (value < 2 || value > 50) {
        throw("Numero de comodos inválidos");
    } else {
        _comodos = value;
    }
  }

  comodos() {
    return _comodos;
  }
}

void main() {
    casa casa1 = new casa();
    casa1.setComodos(10); //10 comodos
    print(casa1.comodos());
}

If you do so:

    casa casa1 = new casa();
    casa1.setComodos(100); //100 comodos
    print(casa1.comodos());

It will issue a custom Exception that states that the number of guest rooms is invalid, something like:

Unhandled exception:
Numero de comodos inválidos
#0      casa.setComodos (file:///home/brcontainer/prog.dart:9:6)
#1      main (file:///home/brcontainer/prog.dart:22:11)
#2      _startIsolate.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:261)
#3      _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:148)

---

About private (variable visibility) on Dart

Dart will treat variables as private as long as the class is in a separate lib and use underline/underscore as prefix if the class is declared in the same document of main(), see the documentation:

• https://dart.dev/guides/language/language-tour#Libraries-and-visibility