Answer.

VB.NET supports operator overloading, which allows defining custom behavior for standard operators (+, -, =, <, >, etc.) when working with user-defined types. This is achieved using the Operator keyword and declaring a special method in a class or structure.

Example (overloading the "+" operator):

Public Structure Vector2D
    Public X As Double
    Public Y As Double

    Public Sub New(x As Double, y As Double)
        Me.X = x
        Me.Y = y
    End Sub

    Public Shared Operator +(a As Vector2D, b As Vector2D) As Vector2D
        Return New Vector2D(a.X + b.X, a.Y + b.Y)
    End Operator
End Structure

Limitations and rules:

• Only a limited number of operators can be overloaded (arithmetic, comparison, etc.).
• Operators must always be defined as Public Shared (static).
• Operator methods must have the expected signature (usually two parameters of the appropriate type and a return value of the same type).
• Not all operators are allowed to be overloaded (for example: = for assignment cannot be overloaded, only for comparison).

Error — ambiguity: operator overloading makes the code "magical": interviewees might not guess why user-defined objects can be added.

Trick question.

Why is it impossible to overload the assignment operator ":=" or "=" but only the comparison operator "=" in Visual Basic .NET?

Answer: In VB.NET, the assignment operator (=) cannot be overloaded, only the comparison operator. This corresponds to the semantics and architecture of the language — overloading the rules of the base assignment operator is not allowed, as it violates the fundamental logic of the language. However, the comparison (equality) operator can be overloaded for user-defined types:

Public Shared Operator =(a As MyClass, b As MyClass) As Boolean
    Return a.ID = b.ID
End Operator

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History

A developer created a class for currency amounts and overloaded the + operator, not implementing a corresponding -. When trying to subtract amounts in the client code, they encountered "Operator '-' is not defined for type 'Money'" — half of the modules stopped working.

History

An employee was trying to overload "=" and was convinced that they were changing the logic of assignment, but actually changed the behavior of comparison. This led to the collection of objects behaving strangely: comparison using "=" returned unexpected results, while assignment was not overloaded at all.

History

In a project involving vector algebra, all possible operators were overloaded, including comparisons, without also implementing GetHashCode and Equals. Hash tables and SortedLists started behaving incorrectly: objects were not found by keys, leading to issues with collections.