Explicit casting

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Diffident - 27 Nov 2006 19:55 GMT

Hello All,

Is it only a best practice to use "AS" or "IS" or are there any performance
benefits to using these over explicit casting?

Thanks for your clarifications!

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Michael Nemtsev - 27 Nov 2006 20:50 GMT

Hello Diffident,

http://groups.google.com/group/microsoft.public.dotnet.languages.csharp/browse_f
rm/thread/5b2c8fda8998aa85/f3ef3e62bf06a929

D> Is it only a best practice to use "AS" or "IS" or are there any
D> performance benefits to using these over explicit casting?

---
WBR,
Michael Nemtsev [C# MVP] :: blog: http://spaces.live.com/laflour

"At times one remains faithful to a cause only because its opponents do not
cease to be insipid." (c) Friedrich Nietzsche

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Gabriel Lozano-Morán - 28 Nov 2006 00:17 GMT

The is and as keywords are used for what is called RunTime Type
Identification (RTTI). I recommend Jeffrey Richter's book CLR via C# where
he explains what happens exactly behind the scenes.

Gabriel

> Hello All,
>
[quoted text clipped - 3 lines]
>
> Thanks for your clarifications!

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Manish Bafna - 09 Dec 2006 22:34 GMT

Hi,
Yes there are performance benefits of using keywords "as" and "is".Because
keyword "is" does not use relection it is much faster.You will find in detail
about performance benefits of keyword "as" and "is" in the following URL:

http://gabewishnie.blogspot.com/2005/10/is-and-as-lesser-known-c-keywords.html

Thanks and Regards,
manish bafna

> Hello All,
>
> Is it only a best practice to use "AS" or "IS" or are there any performance
> benefits to using these over explicit casting?
>
> Thanks for your clarifications!

Reply to this Message

Ben Voigt - 11 Dec 2006 18:13 GMT

> Hi,
> Yes there are performance benefits of using keywords "as" and "is".Because
> keyword "is" does not use relection it is much faster.You will find in
> detail

faster than GetType, yes. Faster than a cast, not unless the cast invokes a
user-defined conversion, in which is/as will fail.

> about performance benefits of keyword "as" and "is" in the following URL:
>
> http://gabewishnie.blogspot.com/2005/10/is-and-as-lesser-known-c-keywords.html

You may want to rely on expert sources. That blog incorrectly asserts that
"is" and "as" use the same MSIL instruction, whereas there are two separate
instructions "isinst" and "castclass".

In addition, while "is" works perfectly well in the examples shown in that
blog, it is not equivalent. For example:
object s = "ABC";
s.GetType() == typeof(object); // false
s is object; // true

> Thanks and Regards,
> manish bafna
[quoted text clipped - 6 lines]
>>
>> Thanks for your clarifications!

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Explicit casting

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