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Cast using AS keyword

Cînd dorești să faci un cast .NET iți oferă mai multe posibilități. Astăzi o să vorbim despre doua dintre ele, varianta clasica, folosind paranteze și cea folosind AS.
Mod de folosire:
IEntity entity=(IEntity)student;
sau
IEntity entity=student as IEntity;
if(entity==null)
{
//do something.
}else
{
...
}
Cînd se foloseste AS trebuie sa fim atenți in cazul in care cast-ul nu se poate face, moment in care variabila o sa aibe valoarea NULL. In general o sa fie nevoie sa se verifice daca cast-ul s-a putut face sau nu.In cele mai multe scenarii din lumea reala, o sa avem nevoie ca o exceptie sa fie aruncata, deoarece este posibil ca un alt tip sau assembly sa fi fost folosit. Sunt momente cand AS isi gaseste locul. In metodele private unde s-a facut deja o validare a datelor folosite sau avem certitudinea ca datele primite sunt asa cum ne asteptam.
Dar AS mai ascunde ceva, o problema de performanta. Mecanismul care sta in spate nu este magic deloc. In spate se face o verificare simpla, dacă conversia se poate face sau nu, iar in cazul in care acesta nu se poate face se returnează null. Ceva ce noi am putea implementa in felul urmator:
IEntity=entity is IEntity?(IEntity)entity:null;
Din cauza la acesta verificare in plus AS este mai lent cu circa 40%. Dar asta nu ii un motiv să nu îl folosim in aplicațiile de zi cu zi. Probleme de performanta nu ar trebuii să apară in general, dar este bine să se tina cont de acest lucru cînd se scrie o bucata de cod unde performanta este critica.
Pentru teste am folosit următorul cod( click pe imagine pentru a vedea codul):
Părerea mea personala este să nu folosiți AS, doar in cazuri speciale unde acesta își are rostul. Poate ca pare mai ușor de scris ca un cast cu AS, dar acesta poate să cauzeze erori ciudate cauzate de valoarea null, mai ales cînd cast-ul se face într-un loc, iar variabila este apoi folosita într-o alta metoda sau este trimisa mai departe.

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