Why is this an issue?

Most developers expect property access to be as efficient as field access. However, if a property returns a copy of an array or collection, it will be much slower than a simple field access, contrary to the caller’s likely expectations. Therefore, such properties should be refactored into methods so that callers are not surprised by the unexpectedly poor performance.

This rule tracks calls to the following methods inside properties:

• Enumerable.ToList
• Enumerable.ToArray
• Array.Clone

How to fix it

Code examples

Noncompliant code example

Dim foo = {"a", "b", "c" }
Property Foo() As String() ' Noncompliant
    Get
        Dim copy = foo.Clone      ' Expensive call
        Return copy
    End Get
End Property

Compliant solution

Dim foo = {"a", "b", "c" }
Function GetFoo() As String()
    Dim copy = foo.Clone
    Return copy
End Function

Resources

Documentation

• Properties (Visual Basic)
• Fields and properties
• Collections (Visual Basic)