Runtime: Do not use OfType<T>() with impossible types
Warn if use of OfType<T>() would provably result in an empty sequence, because we can see that the input type in the sequence will never be the specified type.
Category: Reliability
Suggested severity: Warning
UPDATE FROM roslyn-analyzer issue :
The following will always throw an InvalidCastException at runtime:
new int[] { 1 }.Cast<string>().ToList();
new float[] { 1f }.Cast<double>().ToList();
new int[] { 1 }.Cast<long>().ToList();
Perhaps worse, this will return an enumerable that fully enumerates the source and then returns no items silently:
enumerableOfApple.OfType<Orange>()
Both of these situations are likely to be a mistake.
Ther is a PR out for review
terrajobst
All 5 comments
Estimates:
- Analyzer: Small
- Fixer: Not Applicable
jeffhandley
on 21 Mar 2020
Possibly at the same time, though via a different diagnostic ID: calling OfType<T>() on an IEnumerable<T> where the T is identical or assignable is redundant.
```c#
Enumerable.Range(1, 100).OfType
// @jnyrup points out that this is actually a non-null check,
// so isn't completely safe to remove
// myString.Split(",").OfType
drewnoakes
on 4 Jun 2020
I did a little prototype for fun over at https://github.com/dotnet/roslyn-analyzers/issues/3608
fowl2
on 4 Jun 2020
@drewnoakes Note that for reference types this can be used as a less clear way of writingWhere(e => e != null).
jnyrup
on 5 Jun 2020
bartonjs
on 10 Nov 2020
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Most helpful comment
Possibly at the same time, though via a different diagnostic ID: calling
OfType<T>()on anIEnumerable<T>where theTis identical or assignable is redundant.```c#();
Enumerable.Range(1, 100).OfType
// @jnyrup points out that this is actually a non-null check,
// so isn't completely safe to remove
// myString.Split(",").OfType