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IComparer generic - propietatea Default

De obicei cand dorim sa putem compara doua obiecte de acelasi tip folosim IComparar. Aceasta ne pune la dispozitie metoda
int Compare(T x, T y);
Valorea returnata de aceasta metoda poate sa fie:
  • >0 - daca x este mai mare ca y;
  • =0 - daca x este egal cu y;
  • <0 - daca x este mai mic ca y;
In cazul in care una( sau amandoua) din valori, metoda poate sa returneze:
  • >0 - daca y este null;
  • =0 - daca x so y sunt null;
  • <0 - daca x este mai mic ca y;
Dar pentru a putea face aceasta comparatie una din valori trebuie sa fie diferita de null, atlfel o sa avem parte de NullReferenceException. Pentru a putea rezolva aceasta problema putem sa avem ceva de genul:
var valoare = x == null ? ( y == null ? 0 : -1 ) : x.CompareTo(y);
Este necesar sa verificam daca una din valor este null. Valoarea lui y nu trebe sa o verificam obligatoriu, dar cea a lui x trebuie sa o verificam mereu.
Pentru a rezolva acest neajuns, avem la dispozitie propietatea Default pe IComparable. Aceasta va crea automat comparatorul default pentru tipul de data dat. De exemplu daca lucram cu un obiect de tip nullable, putem sa evitam sa facem verificarea descrisa mai sus folosind aceasta propietate:
int? x,y;
// ...
var valoare = Comparar<int?>.Default.Compare(x,y);
Acesta va crea instanta in regim de Singleton, o instanta a clasei Comparer. Tipul de data T pe care il folosim trebuie sa implementeze interfata IComparable.
Aceasta propietate ne poate scapa de grijile de a verifica fiecare element daca este null inainte de a face compararea.


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