How Can I Avoid the 'Possible Multiple Enumeration of IEnumerable' Warning in C#?

Dealing with the Perils of Multiple Enumeration of IEnumerable

When working with IEnumerable collections, developers often encounter the warning "Possible multiple enumeration of IEnumerable," which arises when the collection is iterated multiple times. This issue can be problematic, especially when working with certain types of collections, such as those representing database queries or other expensive operations.

Consider the following code snippet:

public List<object> Foo(IEnumerable<object> objects)
{
    if (objects == null || !objects.Any())
        throw new ArgumentException();

    var firstObject = objects.First();
    var list = DoSomeThing(firstObject);        
    var secondList = DoSomeThingElse(objects);
    list.AddRange(secondList);

    return list;
}

One way to avoid the multiple enumeration warning is to modify the method parameter to accept a List