IEnumerable.Cast() vs casting in IEnumerable.Select()

Question

Suppose I have an IEnumerable<int> and I want these to be converted into their ASCII-equivalent characters.

For a single integer, it would just be (char)i, so there's always collection.Select(i => (char)i), but I thought it would be a tad cleaner to use collection.Cast().

Can anyone explain why I get an InvalidCastException when I use collection.Cast<char>() but not with collection.Select(i => (char)i)?

Edit: Interestingly enough, when I call collection.OfType<char>() I get an empty set.

score 12 · Accepted Answer · edited Feb 07 '19 at 18:58

12

The Cast<T> and OfType<T> methods only perform reference and unboxing conversions. So they can't convert one value type to another value type.

The methods operate on the non-generic IEnumerable interface, so they're essentially converting from IEnumerable<object> to IEnumerable<T>. So, the reason you can't use Cast<T> to convert from IEnumerable<int> to IEnumerable<char> is that same reason that you can't cast a boxed int to a char.

Essentially, Cast<char> in your example fails because the following fails:

object ascii = 65;
char ch = (char)ascii;   <- InvalidCastException

See Jon Skeet's excellent EduLinq post for more details.

edited Feb 07 '19 at 18:58

Sinjai

1,085
1
15
34

answered Mar 26 '12 at 03:31

Andrew Cooper

32,176
5
81
116

Thanks! Kinda counter-intuitive, but it makes sense – hehewaffles Mar 26 '12 at 03:34
The link to Jon Skeet's blog appears to be broken. Here's an alternate: http://edulinq.googlecode.com/hg/posts/33-CastAndOfType.html – Tyler Gill Jul 22 '14 at 23:38
@TylerGill, this link is broken too – 3per Oct 26 '16 at 02:50
1

That article keeps moving. Here's an(other) alternate location: http://blogs.msmvps.com/jonskeet/2011/01/13/reimplementing-linq-to-objects-part-33-cast-and-oftype/ – Tyler Gill Oct 26 '16 at 15:34

IEnumerable.Cast() vs casting in IEnumerable.Select()

1 Answers1

Linked