Should I prefer the 'is' or 'as' operator?

Question

Possible Duplicate:
casting vs using the 'as' keyword in the CLR

foreach (MyClass i in x)
{
        if (i is IMy)
        {
                IMy a = (IMy)i;
                a.M1();
        }
}

or

foreach (MyClass i in x)
{
        IMy a = i as IMy;
        if (a != null)
        {
                a.M1();
        }

}

Related: http://stackoverflow.com/questions/496096/casting-vs-using-the-as-keyword-in-the-clr — JYelton, Mar 22 '11 at 20:56

score 16 · Accepted Answer · answered Mar 22 '11 at 20:18

16

Second is more preferable as you cast 1 time

answered Mar 22 '11 at 20:18

Stecya

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Yes, the second is preferred of the two given, but frankly there is a better third option: http://stackoverflow.com/questions/5397311/should-i-prefer-the-is-or-as-operator/5397384#5397384 – jason Mar 22 '11 at 20:40
you can use the inline is keyword : foreach (MyClass i in x) if (i is IMy a) a.M1(); – Derek Tremblay Aug 23 '17 at 22:54

score 10 · Answer 2 · answered Mar 22 '11 at 20:23

10

I prefer a third option:

foreach(var i in x.OfType<IMy>()) {
    i.M1();
}

answered Mar 22 '11 at 20:23

jason

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Whoa, that is pretty cool, short, and to the point. – Emmanuel F Mar 22 '11 at 21:11

score 8 · Answer 3 · answered Mar 22 '11 at 20:24

8

The second, as that only does one cast. Or you can use the OfType method:

foreach (IMy i in x.OfType<IMy>()) {
  i.M1();
}

answered Mar 22 '11 at 20:24

Guffa

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score 3 · Answer 4 · answered Mar 22 '11 at 20:21

3

Second is preferable, as you're casting only once.

This article can also help understand this. 'as' operation does the 'is' check and returns either a casted object or a null - does all the work for you.

answered Mar 22 '11 at 20:21

Kon

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score 3 · Answer 5 · answered Mar 22 '11 at 20:23

3

The second. It's the same number of lines of code but you avoid doing the cast twice.

Note that whilst the second is preferable it wouldn't have worked it the type had been a value type. You can only use as on reference or nullable types.

answered Mar 22 '11 at 20:23

Sean

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Should I prefer the 'is' or 'as' operator?

5 Answers5