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AnswerRe: Exceptions Pin
Eddy Vluggen18-Jan-22 18:02
professionalEddy Vluggen18-Jan-22 18:02 
AnswerRe: Exceptions Pin
jschell23-Jan-22 7:32
Memberjschell23-Jan-22 7:32 
Questionnecessity to use .Any() to check if an IEnumerable<T> result has no items without iterating over it ? Pin
BillWoodruff16-Jan-22 2:39
mveBillWoodruff16-Jan-22 2:39 
GeneralRe: necessity to use .Any() to check if an IEnumerable<T> result has no items without iterating over it ? Pin
harold aptroot16-Jan-22 3:21
Memberharold aptroot16-Jan-22 3:21 
GeneralRe: necessity to use .Any() to check if an IEnumerable<T> result has no items without iterating over it ? Pin
BillWoodruff16-Jan-22 5:14
mveBillWoodruff16-Jan-22 5:14 
GeneralRe: necessity to use .Any() to check if an IEnumerable<T> result has no items without iterating over it ? Pin
harold aptroot16-Jan-22 6:56
Memberharold aptroot16-Jan-22 6:56 
GeneralRe: necessity to use .Any() to check if an IEnumerable<T> result has no items without iterating over it ? Pin
BillWoodruff16-Jan-22 18:22
mveBillWoodruff16-Jan-22 18:22 
GeneralRe: necessity to use .Any() to check if an IEnumerable<T> result has no items without iterating over it ? Pin
Richard Deeming16-Jan-22 22:45
mveRichard Deeming16-Jan-22 22:45 
BillWoodruff wrote:
If an IEnumerable "knew" its count ... is that a contradiction in terms ?
Not really. For example, a List<T> is also an IEnumerable<T>; the List<T> "knows" its count.

The TryGetNonEnumeratedCount method simply attempts to cast the IEnumerable<T> to a few "pre-counted" interfaces at run-time, and returns the Count property from the first one that succeeds. You can see the source code on GitHub:

runtime/Count.cs at 57bfe474518ab5b7cfe6bf7424a79ce3af9d6657 · dotnet/runtime · GitHub[^]

It tries ICollection<T>, IIListProvider<T>, and the non-generic ICollection. That should cover most cases, although it notably doesn't try the IReadOnlyCollection<T> introduced in .NET 4.5 - I can't find an official comment, but this SO thread[^] discusses that.

You can see the original proposal for this method on the runtime repository:
Non-enumerating Count Linq Method · Issue #27183 · dotnet/runtime · GitHub[^]



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GeneralRe: necessity to use .Any() to check if an IEnumerable<T> result has no items without iterating over it ? Pin
BillWoodruff18-Jan-22 1:19
mveBillWoodruff18-Jan-22 1:19 
GeneralRe: necessity to use .Any() to check if an IEnumerable<T> result has no items without iterating over it ? Pin
Richard Deeming18-Jan-22 1:41
mveRichard Deeming18-Jan-22 1:41 
GeneralRe: necessity to use .Any() to check if an IEnumerable<T> result has no items without iterating over it ? Pin
BillWoodruff18-Jan-22 3:08
mveBillWoodruff18-Jan-22 3:08 
GeneralRe: necessity to use .Any() to check if an IEnumerable<T> result has no items without iterating over it ? Pin
Richard Deeming18-Jan-22 6:17
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GeneralRe: necessity to use .Any() to check if an IEnumerable<T> result has no items without iterating over it ? Pin
BillWoodruff19-Jan-22 13:58
mveBillWoodruff19-Jan-22 13:58 
GeneralRe: necessity to use .Any() to check if an IEnumerable<T> result has no items without iterating over it ? Pin
Richard Deeming19-Jan-22 21:43
mveRichard Deeming19-Jan-22 21:43 
GeneralRe: necessity to use .Any() to check if an IEnumerable<T> result has no items without iterating over it ? Pin
BillWoodruff20-Jan-22 4:26
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GeneralRe: necessity to use .Any() to check if an IEnumerable<T> result has no items without iterating over it ? Pin
harold aptroot16-Jan-22 22:48
Memberharold aptroot16-Jan-22 22:48 
GeneralRe: necessity to use .Any() to check if an IEnumerable<T> result has no items without iterating over it ? Pin
BillWoodruff18-Jan-22 0:49
mveBillWoodruff18-Jan-22 0:49 
GeneralRe: necessity to use .Any() to check if an IEnumerable<T> result has no items without iterating over it ? Pin
jschell23-Jan-22 7:40
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GeneralRe: necessity to use .Any() to check if an IEnumerable<T> result has no items without iterating over it ? Pin
BillWoodruff25-Jan-22 3:58
mveBillWoodruff25-Jan-22 3:58 
GeneralRe: necessity to use .Any() to check if an IEnumerable<T> result has no items without iterating over it ? Pin
jschell30-Jan-22 6:22
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