IEnumerable or IList: How to Avoid Multiple Enumeration Warnings?

Navigating Multiple Enumeration Warnings When Using IEnumerable

Challenge:

Working with an IEnumerable requires consideration of potential multiple enumerations. In certain scenarios, this can trigger the ReSharper warning of "Possible multiple enumeration of IEnumerable."

Possible Solutions:

Changing the parameter to a List type sidesteps the warning but may restrict access to specific objects. Converting the IEnumerable to a List at the method's outset resolves the issue but introduces the perception of awkwardness.

Recommended Approach:

The primary concern with using IEnumerable as a parameter stems from its ambiguity regarding the number of enumerations intended. Modifying the method signature to specify IList or ICollection clarifies expectations for callers and prevents costly mistakes.

Alternatively, performing the .ToList() conversion at the method's start might be appropriate if using IEnumerable is crucial. However, this approach may be less efficient than specifying a more restrictive parameter type.

Additional Considerations:

The ideal solution would involve an interface that combines the functionality of IEnumerable, Count, and Indexer but excludes mutating methods. Unfortunately, such an interface currently does not exist in .NET, leaving us to weigh the pros and cons of each approach based on specific usage requirements.

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