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Definirea unui mecanism de comparare a entitatiilor din punct de vedere a structurii folosind IStructuralEquatable

Uneori avem nevoie sa putem compara clasele de tip POCO ca pe niste structuri. De exemplu daca avem clasa Student, dorim sa comparam entitatile de acest tip din punct de vedere a datelor pe care le contin.
class Student
{
public string Nume{ get;set;}
public string Prenume{ get;set;}
public int Varsta{ get;set;}
}
Pentru acest lucru sa folosim IStructuralEquatable. Aceasta interfata a fost creata pentru a fi folosita in tupluri. In cazul acestora, doua tupluri sunt egale daca fiecare element din tuplu este egal din celalalt tuplu.
Interfata contine doua metode:
bool Equals(Object other, IEqualityComparer comparer);
int GetHashCode(IEqualityComparer comparer);
Prin intermediul parametrului comparer se defineste mecanismul de comparare. Exista cateva implementari in .NET pentru IEqualityComparer prin care putem sa comparam siruriile de elemente - element cu element.
Valoarea default a acestui parametru este EqualityComparer>Object<.Default.Equals in cazul in care se foloseste mecanismul standard de comparare. O alta implementare este StructuralComparisons.StructuralEqualityComparer. Aceasta este folosita cand lucram cu tupluri sau cu clase ce implementeaza IStructuralEquatable.
Dar ne putem defini si noi propriul mecanism de comparare daca implementam IEqualityComparer. De exemplu in cazul nostru am putea sa avem:
public class FullNameComparer
{
public new bool Equals(object s1, object s2)
{
...
var student1 = s1 as Student;
var student2 = s2 as Student;
return student1.Nume == student2.Nume && student1.Prenume == student2.Prenume;
}
}
Pentru a putea compara doi studenti putem sa apelam( clasa Student trebuie sa implementeze IStructuralEquatable):

var student1 = new Student() { ... };
var student2 = new Student() { ... };
bool areEquals = student1.Equals(student2, new FullNameComparer());
Unde ne este utiliza aceasta interfata. Cand avem nevoie sa definim mai multe mecanism de comparare pentru o clasa de un anumit fel. Prin acest mecanism putem foarte usor sa trimitem printr-un parametru modul in care sa se faca compararea. Cel mai bine aceasta interfata se preteaza cand lucram cu tupluri.
Exista nenumarate solutii la aceasta problema, depinde de la caz.

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