How to Convert a List to a List in .NET?

Transforming List to List in .NET

This guide explains how to convert a list of Client objects (List<Client>) into a list of their corresponding IDic interfaces (List<IDic>).

Why Direct Casting Fails

Direct casting from a derived type (like Client) to a base type (IDic) is permitted in .NET. However, the reverse is not straightforward due to covariance limitations. These restrictions prevent unsafe operations where a base-type list could unexpectedly contain derived-type elements, preserving type safety.

Effective Conversion Methods

Two reliable methods achieve the desired conversion:

1. Leveraging IEnumerable<IDic> ( .NET 4 and later)

.NET 4 and later versions support covariance with IEnumerable<T>. This enables conversion from List<Client> to IEnumerable<IDic>, allowing iteration over Client objects as IDic instances.

2. Constructing a New List

To create a List<IDic>, you must explicitly build a new list and populate it with the interface references. .NET 4 offers the ToList<T>() method for this. .NET 3.5 utilizes Cast<T>() followed by ToList().

Important Note on Data Independence

Both techniques generate separate lists, maintaining type safety. Crucially, modifications to the original List<Client> will not automatically update the new List<IDic>. Only changes directly made to the Client objects themselves will be visible in both lists.

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