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IIF In C#?
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De
18/03/2010 05:54:45
 
 
À
18/03/2010 05:16:54
Information générale
Forum:
ASP.NET
Catégorie:
Code, syntaxe and commandes
Titre:
Divers
Thread ID:
01455229
Message ID:
01455310
Vues:
45
>>>>>>>Any way to do this in C# like VFP's IIF()?
>>>>>>>
>>>>>>>
>>>>>>>if (Checked)
>>>>>>>{
>>>>>>>    _CheckItemsCount++;
>>>>>>>}
>>>>>>>else
>>>>>>>{
>>>>>>>    _CheckItemsCount--;
>>>>>>>}
>>>>>>>
>>>>>>
>>>>>>
_CheckedItemsCount+=    (Checked) ? 1:-1;
>>>>>
>>>>>IMHO, this is harder to read than the original.
>>>>
>>>>Probably because you're not used to reading it :-}
>>>
>>>For sure it's in the eyes - and experience - of the beholder.
>>>
>>>The C/C++/C# conditional operator is so useful I'd bet it's widely implemented in other languages, too. But so is IF... etc.
>>>
>>>It could be argued that for simple cases like this the *only* significant consideration is readability/maintainability. Any decent optimizing compiler (JIT or otherwise) will probably spit out identical opcode for those two snippets.
>>
>>I don't think that the first version can be optimized to the same code in this case - it needs to add or subtract based on the condition whilst the second always adds. In fact the code size for the first is 40, for the second 24, FWIW here's the CIL:
.method private hidebysig static void  TestA() cil managed
>>{
>>  // Code size       40 (0x28)
>>  .maxstack  2
>>  .locals init ([0] bool CS$4$0000)
>>  IL_0000:  nop
>>  IL_0001:  ldsfld     bool ConsoleApplication2.Program::Checked
>>  IL_0006:  ldc.i4.0
>>  IL_0007:  ceq
>>  IL_0009:  stloc.0
>>  IL_000a:  ldloc.0
>>  IL_000b:  brtrue.s   IL_001b
>>  IL_000d:  ldsfld     int32 ConsoleApplication2.Program::_CheckItemsCount
>>  IL_0012:  ldc.i4.1
>>  IL_0013:  add
>>  IL_0014:  stsfld     int32 ConsoleApplication2.Program::_CheckItemsCount
>>  IL_0019:  br.s       IL_0027
>>  IL_001b:  ldsfld     int32 ConsoleApplication2.Program::_CheckItemsCount
>>  IL_0020:  ldc.i4.1
>>  IL_0021:  sub
>>  IL_0022:  stsfld     int32 ConsoleApplication2.Program::_CheckItemsCount
>>  IL_0027:  ret
>>} // end of method Program::TestA
v
.method private hidebysig static void  TestB() cil managed
>>{
>>  // Code size       24 (0x18)
>>  .maxstack  8
>>  IL_0000:  nop
>>  IL_0001:  ldsfld     int32 ConsoleApplication2.Program::_CheckItemsCount
>>  IL_0006:  ldsfld     bool ConsoleApplication2.Program::Checked
>>  IL_000b:  brtrue.s   IL_0010
>>  IL_000d:  ldc.i4.m1
>>  IL_000e:  br.s       IL_0011
>>  IL_0010:  ldc.i4.1
>>  IL_0011:  add
>>  IL_0012:  stsfld     int32 ConsoleApplication2.Program::_CheckItemsCount
>>  IL_0017:  ret
>>} // end of method Program::TestB
>
>Interesting. I'd have thought an optimizer would deem the two equivalent, but evidently not.
>
>Out of interest, is there any difference using prefix instead of postfix, or a plain old x = x + 1 and x = x - 1 ?

I know that ' x = x + 1' does compile to the same as 'x++'' ( I'd assume x=x-1 would behave the same but haven't looked) so that's not what causes the difference in the above example. The first one has to branch to perform either an add or subtract instruction - the second just pulls a different value for the same add operation (@ IL_0011)


>No doubt there are other ways to do this :-\
I'll admit that once I start nesting ? : conditions readability does take a dive :-{
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