Properties should not return arrays
TypeName |
PropertiesShouldNotReturnArrays |
CheckId |
CA1819 |
Category |
Microsoft.Performance |
Breaking Change |
Breaking |
Cause
A public or protected property in a public type returns an array.
Rule Description
Arrays returned by properties are not write-protected, even if the property is read-only. To keep the array tamper-proof, the property must return a copy of the array. Typically, users will not understand the negative performance implications of calling such a property. Specifically, they might use the property as an indexed property.
How to Fix Violations
To fix a violation of this rule, make the property a method.
When to Exclude Warnings
Do not exclude a warning from this rule.
Example
The following example shows a property that violates this rule. The Main method illustrates how a user might write poorly performing code using such a property.
Imports System
Namespace PerformanceLibrary
Public Class Test
Private nameValues() As String
Public Sub New()
nameValues = New String(100) {}
' Loading string array with sample data.
Dim i As Integer
For i = 0 To 99
nameValues(i) = "Sample"
Next i
End Sub 'New
' Violates rule: PropertiesShouldNotReturnArrays.
Public ReadOnly Property Names() As String()
Get
Return CType(nameValues.Clone(), String())
End Get
End Property
Public Shared Sub Main()
' Using the property in the following manner
' results in 201 copies of the array.
' One copy is made each time the loop executes,
' and one copy is made each time the condition is tested.
Dim t As New Test()
Dim i As Integer
For i = 0 To t.Names.Length - 1
If t.Names(i) = "SomeName" Then
' Perform some operation.
End If
Next i
End Sub 'Main
End Class 'Test
End Namespace
using System;
namespace PerformanceLibrary
{
public class Test
{
string [] nameValues;
public Test()
{
nameValues = new string[100];
// Loading string array with sample data.
for (int i = 0; i< 100; i++)
{
nameValues[i] = "Sample";
}
}
// Violates rule: PropertiesShouldNotReturnArrays.
public string [] Names
{
get
{
return (string[]) nameValues.Clone();
}
}
public static void Main()
{
// Using the property in the following manner
// results in 201 copies of the array.
// One copy is made each time the loop executes,
// and one copy is made each time the condition is tested.
Test t = new Test();
for (int i = 0; i < t.Names.Length ; i++)
{
if (t.Names[i] == ("SomeName"))
{
// Perform some operation.
}
}
}
}
}