Cast() or OfType() in LINQ: When Should I Use Which?

The difference between Cast() and OfType() in LINQ: in-depth understanding

In LINQ, when working with collections that may contain elements of different types, you may need to convert the entire collection to a specific type. LINQ provides two methods for this purpose: Cast() and OfType().

Cast() method

Cast() attempts to convert all elements in the collection to the specified type. If any element cannot be successfully cast, an InvalidCastException is thrown. This method is useful when you are sure that all elements in the collection can be converted to the required type.

OfType() method

Unlike Cast(), OfType() only returns elements in the collection that can be safely cast to the specified type. It doesn't try to convert all elements, so no exception is thrown. This method is useful when you only want to filter out elements that can be converted.

Example usage

Consider the following code:

<code class="language-csharp">object[] objs = new object[] { "12345", 12 };</code>

If you try to use Cast() to convert this array to a collection of strings, you will receive an InvalidCastException because one of the elements is an integer.

<code class="language-csharp">IEnumerable<string> someCollection = objs.Cast<string>();</code>

However, if you use OfType(), it will only return elements that can be safely converted to a string.

<code class="language-csharp">IEnumerable<string> someCollection = objs.OfType<string>();</code>

In this case, someCollection will contain only one element: "12345".

Summary

Cast() and OfType() are two LINQ methods that serve different purposes when working with mixed-type collections. Cast() attempts to cast all elements, while OfType() only selects elements that are safe to cast. Use Cast() when you're sure about type casting; use OfType() when you just want to filter out valid elements.

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