DART somo la 40: factory constructor

Aina ya constructor ambayo tumkuwa tukiitumia toka huko mwanzo inaitwa ganerative constructor hii ina mfanano na factory constructor, ila kwenye generative constructor yenyewe inaweza kutengeneza instance of calss tu yaani object lakini hii ya factory constructor inawez akute geneza instance of class na  subclass.

Factory constructory hutengenezwa kwa kutumia keyword factory ikifuatiwa na jina la class kama tulivyoona kwenye generative constructor. pia factory constructory inaweza kuwa named.

class gari {

 factory gari() {

 }

 factory toyota.gari() {

 }

}

Hapa nitakupa mfano mmoja ambao kwanza nitatuia generative constructor kama tulivyo zoea kisha nitatumia factoru constructory.

class eneo {

 final int urefu;

 final int upana;

 final int jibu;

 // constructor

 const eneo(this.urefu, this.upana) : jibu = urefu * upana;

}

void main() {

 eneo en = eneo(12, 4);

 print("Eneo ni: ${en.jibu}");

}

Sasa wacha tuone jinsi ya kutumia mfano uliotamgulia kwenye factory constructor.

class Eneo {

 final int urefu;

 final int upana;

 final int jibu;

 // Regular constructor

 const Eneo._internal(this.urefu, this.upana, this.jibu);

 // Factory constructor

 factory Eneo(int urefu, int upana) {

   int jibu = urefu * upana;

   // Return an instance using the private constructor

   return Eneo._in...