Why Does Adding a New Value to a List Overwrite Previous Values When Using Reference Types?

Understanding List Overwrites with Reference Types

The provided code demonstrates a common pitfall when using reference types with lists. The Tag class, being a reference type, means variables hold a reference to the object's memory location, not a copy of the object itself.

Within the loop, the same _tag instance is repeatedly modified. Each addition to the list doesn't create a new Tag object; instead, it adds another reference to the same _tag object. Therefore, the final list contains multiple references pointing to the last modified state of _tag.

Why Using struct Solves the Problem

Changing public class Tag to public struct Tag resolves the issue because structs are value types. When a struct is assigned, a copy of the struct's data is created. Consequently, each iteration of the loop creates a completely independent _tag instance. Modifications to one instance don't affect others, resulting in a list with unique Tag objects.

Derived Collection Class Relevance

The problem isn't inherent to the TagCollection class's design. The TagCollection class itself appears correctly implemented. The core issue lies in how the _tag instance is handled within the loop that populates the list, specifically the repeated modification of a single reference type instance.

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