Question

My co-worker said that in a previous interview, he learned that foreach is faster in VB.Net than c#’s foreach. He was told that this was because both have different CLR implementation.

Coming from a C++ perspective, I’m curious on why this is and I was told that I need to read up on CLR first. Googling foreach and CLR doesn’t help me understand.

Does anyone have a good explanation on why foreach is faster in VB.Net than in c#? Or was my co-worker misinformed?

Answer 1

There is no significant difference at the IL level between C# and VB.Net. There are some additional Nop instructions thrown in here and there between the two versions, but nothing that actually changes what is going on.

Here is the method: (in C#)

public void TestForEach()     {         List<string> items = new List<string> { 'one', 'two', 'three' };          foreach (string item in items)         {             Debug.WriteLine(item);         }     } 

And in VB.Net:

Public Sub TestForEach     Dim items As List(Of String) = New List(Of String)()     items.Add('one')     items.Add('two')     items.Add('three')     For Each item As string In items         Debug.WriteLine(item)     Next End Sub 

Here is the IL for the C# version:

.method public hidebysig instance void TestForEach() cil managed {     .maxstack 2     .locals init (         [0] class [mscorlib]System.Collections.Generic.List`1<string> items,         [1] string item,         [2] class [mscorlib]System.Collections.Generic.List`1<string> <>g__initLocal3,         [3] valuetype [mscorlib]System.Collections.Generic.List`1/Enumerator<string> CS$5$0000,         [4] bool CS$4$0001)     L_0000: nop      L_0001: newobj instance void [mscorlib]System.Collections.Generic.List`1<string>::.ctor()     L_0006: stloc.2      L_0007: ldloc.2      L_0008: ldstr 'one'     L_000d: callvirt instance void [mscorlib]System.Collections.Generic.List`1<string>::Add(!0)     L_0012: nop      L_0013: ldloc.2      L_0014: ldstr 'two'     L_0019: callvirt instance void [mscorlib]System.Collections.Generic.List`1<string>::Add(!0)     L_001e: nop      L_001f: ldloc.2      L_0020: ldstr 'three'     L_0025: callvirt instance void [mscorlib]System.Collections.Generic.List`1<string>::Add(!0)     L_002a: nop      L_002b: ldloc.2      L_002c: stloc.0      L_002d: nop      L_002e: ldloc.0      L_002f: callvirt instance valuetype [mscorlib]System.Collections.Generic.List`1/Enumerator<!0> [mscorlib]System.Collections.Generic.List`1<string>::GetEnumerator()     L_0034: stloc.3      L_0035: br.s L_0048     L_0037: ldloca.s CS$5$0000     L_0039: call instance !0 [mscorlib]System.Collections.Generic.List`1/Enumerator<string>::get_Current()     L_003e: stloc.1      L_003f: nop      L_0040: ldloc.1      L_0041: call void [System]System.Diagnostics.Debug::WriteLine(string)     L_0046: nop      L_0047: nop      L_0048: ldloca.s CS$5$0000     L_004a: call instance bool [mscorlib]System.Collections.Generic.List`1/Enumerator<string>::MoveNext()     L_004f: stloc.s CS$4$0001     L_0051: ldloc.s CS$4$0001     L_0053: brtrue.s L_0037     L_0055: leave.s L_0066     L_0057: ldloca.s CS$5$0000     L_0059: constrained [mscorlib]System.Collections.Generic.List`1/Enumerator<string>     L_005f: callvirt instance void [mscorlib]System.IDisposable::Dispose()     L_0064: nop      L_0065: endfinally      L_0066: nop      L_0067: ret      .try L_0035 to L_0057 finally handler L_0057 to L_0066 } 

Here is the IL for the VB.Net version:

.method public instance void TestForEach() cil managed {     .maxstack 2     .locals init (         [0] class [mscorlib]System.Collections.Generic.List`1<string> items,         [1] string item,         [2] valuetype [mscorlib]System.Collections.Generic.List`1/Enumerator<string> VB$t_struct$L0,         [3] bool VB$CG$t_bool$S0)     L_0000: nop      L_0001: newobj instance void [mscorlib]System.Collections.Generic.List`1<string>::.ctor()     L_0006: stloc.0      L_0007: ldloc.0      L_0008: ldstr 'one'     L_000d: callvirt instance void [mscorlib]System.Collections.Generic.List`1<string>::Add(!0)     L_0012: nop      L_0013: ldloc.0      L_0014: ldstr 'two'     L_0019: callvirt instance void [mscorlib]System.Collections.Generic.List`1<string>::Add(!0)     L_001e: nop      L_001f: ldloc.0      L_0020: ldstr 'three'     L_0025: callvirt instance void [mscorlib]System.Collections.Generic.List`1<string>::Add(!0)     L_002a: nop      L_002b: nop      L_002c: ldloc.0      L_002d: callvirt instance valuetype [mscorlib]System.Collections.Generic.List`1/Enumerator<!0> [mscorlib]System.Collections.Generic.List`1<string>::GetEnumerator()     L_0032: stloc.2      L_0033: br.s L_0045     L_0035: ldloca.s VB$t_struct$L0     L_0037: call instance !0 [mscorlib]System.Collections.Generic.List`1/Enumerator<string>::get_Current()     L_003c: stloc.1      L_003d: ldloc.1      L_003e: call void [System]System.Diagnostics.Debug::WriteLine(string)     L_0043: nop      L_0044: nop      L_0045: ldloca.s VB$t_struct$L0     L_0047: call instance bool [mscorlib]System.Collections.Generic.List`1/Enumerator<string>::MoveNext()     L_004c: stloc.3      L_004d: ldloc.3      L_004e: brtrue.s L_0035     L_0050: nop      L_0051: leave.s L_0062     L_0053: ldloca.s VB$t_struct$L0     L_0055: constrained [mscorlib]System.Collections.Generic.List`1/Enumerator<string>     L_005b: callvirt instance void [mscorlib]System.IDisposable::Dispose()     L_0060: nop      L_0061: endfinally      L_0062: nop      L_0063: ret      .try L_002c to L_0053 finally handler L_0053 to L_0062 }