Those of us who\'ve worked in VB/VB.NET have seen code similar to this abomination:
Dim name As String = IIf(obj Is Nothing, \"\", obj.Name)
<
The main thing is that you correctly identified the new If
as an operator rather than a function. It is also typesafe and therefore does not need boxing, and is a direct mapping to the conditional/ternary/? operator in C/C++/C#/Java/etc
Even without the new operator, you can get some improvement in VB.Net with this code:
Public Shared Function IIf(Of T)(ByVal Expression As Boolean, ByVal TruePart As T, ByVal FalsePart As T) As T
If Expression Then Return TruePart Else Return FalsePart
End Function
Joel beat me to an answer, but here is a sample program and the generated IL that demonstrates that If() passes through to the IL's underlying ternary operator without boxing.
Public Class Test
Public Sub New()
Dim rnd = New Random()
Dim result As Integer = If(rnd.Next(1000) < 500, 1, -1)
Console.WriteLine(result)
End Sub
End Class
As you can see the IL has no 'box' statement.
.method public specialname rtspecialname instance void .ctor() cil managed
{
.maxstack 2
.locals init (
[0] int32 result,
[1] class [mscorlib]System.Random rnd)
L_0000: nop
L_0001: ldarg.0
L_0002: call instance void [mscorlib]System.Object::.ctor()
L_0007: nop
L_0008: newobj instance void [mscorlib]System.Random::.ctor()
L_000d: stloc.1
L_000e: ldloc.1
L_000f: ldc.i4 0x3e8
L_0014: callvirt instance int32 [mscorlib]System.Random::Next(int32)
L_0019: ldc.i4 500
L_001e: blt.s L_0023
L_0020: ldc.i4.m1
L_0021: br.s L_0024
L_0023: ldc.i4.1
L_0024: stloc.0
L_0025: ldloc.0
L_0026: call void [mscorlib]System.Console::WriteLine(int32)
L_002b: nop
L_002c: nop
L_002d: ret
}
Given the same program but using the older IIf() function, the following IL is produced. You can see both the boxing, and the function call overhead:
.method public specialname rtspecialname instance void .ctor() cil managed
{
.maxstack 3
.locals init (
[0] int32 result,
[1] class [mscorlib]System.Random rnd)
L_0000: nop
L_0001: ldarg.0
L_0002: call instance void [mscorlib]System.Object::.ctor()
L_0007: nop
L_0008: newobj instance void [mscorlib]System.Random::.ctor()
L_000d: stloc.1
L_000e: ldloc.1
L_000f: ldc.i4 0x3e8
L_0014: callvirt instance int32 [mscorlib]System.Random::Next(int32)
L_0019: ldc.i4 500
L_001e: clt
L_0020: ldc.i4.1
L_0021: box int32
L_0026: ldc.i4.m1
L_0027: box int32
L_002c: call object [Microsoft.VisualBasic]Microsoft.VisualBasic.Interaction::IIf(bool, object, object)
L_0031: call int32 [Microsoft.VisualBasic]Microsoft.VisualBasic.CompilerServices.Conversions::ToInteger(object)
L_0036: stloc.0
L_0037: ldloc.0
L_0038: call void [mscorlib]System.Console::WriteLine(int32)
L_003d: nop
L_003e: nop
L_003f: ret
}