Are Mutable Structs in C# Evil, and Why Should You Consider Immutable Alternatives?

C# variable structure trap: a warning story

In the field of C# programming, variable structures occupy a controversial position. Some developers advocate the use of them, while others have strongly condemned them as the root cause of potential problems. This article aims to clarify the fundamental issues around the variable structures, and why they get the infamous "evil" name.

Understand value type

Structure, like the original data type (such as int, double), is classified as a value type. This means that when the structure is passed to a function or assignment to a variable, a copy of a original structure will be created. This behavior is different from the reference type (such as class). The reference type is passed according to reference, which means that the changes made by the reference type variable will affect all instances of the same reference.

variability and side effects

The definition of variable structures is that it allows to change its field, even after copying. This attribute may lead to accidents and side effects and make it difficult to infer code behavior. Consider the following example:

In this example, the structure Point is variable, and its X field is modified in the Modifypoint function. The expected result is that the original Point variable P will also be updated. However, the value printed by the console is 1, indicating that the copy passed to Modifypoint is the only modified. (Note: The original example code is wrong, the modified code shows the expected behavior)

Maintain consistency

<code class="language-csharp">public struct Point
{
    public int X;
    public int Y;
}

public void ModifyPoint(Point point)
{
    point.X++;
}

Point p = new Point { X = 1, Y = 2 };
ModifyPoint(p);

Console.WriteLine(p.X); // 1 (预期输出)</code>

Variable structures may make the consistency between multiple copies that are difficult to maintain. For example, consider the situation of multiple threads accessing variable structures at the same time. If another thread visits the original value before changing, the change made by a thread may not be reflected. This may cause unpredictable behavior and potential data damage.

Unchanged alternative

In order to avoid traps related to variable structures, consider changing the unable variable structure. Once the uncharacteristic structure is created, it cannot be modified. Any change must be completed by creating new examples with data after modification.

This method ensures that the copy of all unchanged structures remain consistent, and simplify the reasoning of procedural behavior by eliminating the possibility of unexpected side effects. Conclusion

Although variable structures can provide better performance advantages than immoral structures, their inherent variability may introduce complexity and unexpected behaviors in the program. By understanding the challenges related to variable structures, developers can make wise decisions and choose the unable variable structure when maintaining the definition and consistency of the code.

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