Operatorii is si as

Costul operatorilor as is is

static void Main(string[] args)
        {
            object obj = new string('s', 1);
            IsDemo(obj);
            AsDemo(obj);
            ExplicitDemo(obj);
        }
 static void IsDemo(object str)
{
 string local = null;

 if (str is string)
 {
  local = (string)str;
 }
}

.method private hidebysig static void  IsDemo(object str) cil managed
{
  // Code size       29 (0x1d)
  .maxstack  2
  .locals init ([0] string local,
           [1] bool CS$4$0000)
  IL_0000:  nop
  IL_0001:  ldnull
  IL_0002:  stloc.0
  IL_0003:  ldarg.0

-- parametrul este incarcat si se testeaze daca este de tip System.String

  IL_0004:  isinst     [mscorlib]System.String
  IL_0009:  ldnull

-- se incarca pe stiva rezultatul operatiei IL_0004 > IL_0009 (in acest caz e 1)

  IL_000a:  cgt.un
  IL_000c:  ldc.i4.0
  IL_000d:  ceq

-- se calculeaza IL_000a == IL_000a (adica 1 == 0) si se pastreaza rezultatul in loc.1

  IL_000f:  stloc.1
  IL_0010:  ldloc.1

-- daca este adevarat (1 == 0) se sare la instructiunea IL_001c, in acest caz nu se sare

  IL_0011:  brtrue.s   IL_001c
  IL_0013:  nop
  IL_0014:  ldarg.0

-- castul e sigur si se poate face fara aruncarea exceptiei
InvalidCastException

  IL_0015:  castclass  [mscorlib]System.String
  IL_001a:  stloc.0
  IL_001b:  nop
  IL_001c:  ret
} // end of method Program::IsDemo

static void AsDemo(object str)
{
  string local = str as string;
}

.method private hidebysig static void  AsDemo(object str) cil managed
{
  // Code size       9 (0x9)
  .maxstack  1
  .locals init ([0] string local)
  IL_0000:  nop
  IL_0001:  ldarg.0

-- se testeaza daca clasa obiectului incarcat la IL_0001 este un tip derivat al clasei System.String (System.String este derivat din System.String); daca in loc de System.String ar fi fost o interfata testul se rezuma la faptul daca clasa obiectului implementeaza respectiva interfata. In caz de succes se va face castul la System.String. Altfel este incarcat null. Daca obiectul in sine e null, la fel este incarcat null. Nici o exceptie nu e aruncata la runtime (doar la compilare in cazul in care tipul clasei sau interfetei nu este cunoscut de catre compilator se va da o exceptie TypeLoadException)

  IL_0002:  isinst     [mscorlib]System.String
  IL_0007:  stloc.0
  IL_0008:  ret
} // end of method Program::AsDemo

static void ExplicitDemo(object str)
{
   string local = (string)str;
}

.method private hidebysig static void  ExplicitDemo(object str) cil managed
{
  // Code size       9 (0x9)
  .maxstack  1
  .locals init ([0] string local)
  IL_0000:  nop
  IL_0001:  ldarg.0

--Se incearca a se face castul obiectului la clasa System.String. In caz de testul e fara succes va fi aruncata exceptia InvalidCastException. In caz ca obiectul asupra caruia se face castul e null, operatia de cast se considera OK si e returnat noul obiect ca referinta nula (adica null).

  IL_0002:  castclass  [mscorlib]System.String
  IL_0007:  stloc.0
  IL_0008:  ret
} // end of method Program::ExplicitDemo

valoarea medie la fiecare 10 000 iteratii in nanosecunde
Cast cu "is"Cast cu "as"Explicit castString de test
610.21722034504451.766355779854749.7828634644906a
21.483177331197113.912382719032712.3200015644446aa
20.226034314417113.940319230516712.3758745874126aaa
21.455240819713113.912382719032713.2698429549007aaaa
20.253970825901113.940319230516712.3479380759286aaaaa
20.198097802933115.225398758780813.3257159778687aaaaaa
20.253970825901114.024128764968712.3758745874126aaaaaaa
20.281907337385113.968255742000712.4038110988966aaaaaaaa
20.198097802933113.940319230516712.3758745874126aaaaaaaaa
20.253970825901113.968255742000713.7447636501287aaaaaaaaaa

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