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Switch vs Dictionary

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Revin cu cateva informatii suplimentare pe tema switch vs dictionary ca o continuare a postului

Putem-sa-inlocuim-switch-case

In cazul in care avem un switch simplu care nu are nevoie sa sara de la un case la altul, codul IL care se genereaza in spate o sa fie foarte simplu si rapid. Se genereaza ceva de genul:

IL_0002: ldloc.0
IL_0003: switch (
IL_0016,
IL_001e,
IL_0026)
IL_0014: br.s IL_002e

Dar cand de la un case se sare la un alt case deja IL generat se complica si ar fi bine sa se faca un review la cod. Codul generat mai jos este pentru un switch care are cateva case-uri goale( au fost adaugate doar pentru ca sa avem un cod cat mai readeable) si un case ce nu are break. In cazul acesta, pierderea de performanta este de aproape 50%. Sursa: http://weblogs.asp.net/justin_rogers/archive/2004/03/25/95806.aspx

IL_0002: ldloc.0
IL_0003: switch (
IL_002e,
IL_0036,
IL_003e,
IL_0056,
IL_0056,
IL_0056,
IL_0056,
IL_0046,
IL_004e)
IL_002c: br.s IL_0056

Pentru cazul acesta putem folosii dictionarul cu success. Pe partea de value la dictionar, putem folosii o lista de functii, care o sa fie apelate pe rand, cand o sa avem nevoie de un switch fara break. In cazul unor flow-uri mai complexe ar trebui sa ne implementam un mecanism de workflow.

Recomandari pentru switch:

  • blocuri compacte, fiecare case sa aiba break;
  • expresia comparata sa fie de tip enum sau cu int cu valori fixe( fara intervale de genul: 1 .. 20 si 40 .. 100);
  • char in loc de string-uri( si enum in loc de char);

Daca aveti nevoie de performanta, iar continutul din case nu este complex( nu trebuie sa se apeleze si alte blocuri case la randul sau), switch-ul o sa fie mult mai performant. Dar atentie, in cazul in care in expresia de la switch avem string, folosirea unui dictionar, hashtable sau a unui switch o sa aibe rezultate asemanatoare in IL. Switch-ul o sa fie generat pentru expresii de tip string ca si un hashtable.

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