Why Does `Enumerable.Cast` Throw an `InvalidCastException` When Casting `IEnumerable` to `IEnumerable`?

Understanding Enumerable.Cast and InvalidCastException in C#

A common C# error occurs when using Enumerable.Cast<T> to convert an IEnumerable<int> to an IEnumerable<long>. The unexpected InvalidCastException arises despite the apparent type compatibility.

The reason lies in how Enumerable.Cast<T> functions. It's not a specialized method for generic collections; it operates at the IEnumerable level, working with unboxed values.

Therefore, when casting elements from an IEnumerable<int>, each int is already boxed as an object. Attempting to cast a boxed int to a long directly fails, resulting in the InvalidCastException.

The solution is to explicitly cast each element within a query:

<code class="language-csharp">var castedList = list.Select(i => (long)i);</code>

This Select method performs the conversion from int to long for each item, avoiding the boxing issue. This direct cast circumvents the limitations of Enumerable.Cast<T> when dealing with value type conversions.

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