One of the most interesting features in Xojo is the Variant data type. We will explore the so-called “Implicit Conversions,” discuss the pros and cons of using Variants, and analyze when it makes sense to use this data type.
For more detailed information, you can refer to the official Xojo documentation on Variants.
What are Variants?
A Variant in Xojo is a data type that can store any type of data. This means that a variable of type Variant can take on different data types without needing to be explicitly converted. This can be very useful when you want to be flexible, but it can also lead to unexpected problems if not handled correctly.
Basic Example
Var dynamicValue As Variant
dynamicValue = 42 // Integer
dynamicValue = "Hello" // String
dynamicValue = 3.14 // Double
dynamicValue = True // Boolean
dynamicValue = Color.RGB(255, 0, 0) // Color
dynamicValue = New Dictionary("key" : "value") // DictionaryIn the example above, you can see that dynamicValue can take on different data types without the need to explicitly change the type.
Implicit Conversions
Implicit Conversions are automatic type conversions performed by Xojo when using Variants. This means that Xojo tries to interpret the data in a Variant so that it fits the context in which it is used.
Example of an Implicit Conversion
Var dynamicValue As Variant = "123"
Var myInteger As Integer
myInteger = dynamicValue // Implicit conversion from String to IntegerIn this example, the string “123” is automatically converted to an integer when assigned to the integer variable myInteger.
Another Example with Data Types
Var dynamicValue As Variant = "3.14159"
Var myDouble As Double
myDouble = dynamicValue // Implicit conversion from String to DoubleHere, the string “3.14159” is automatically converted to a double. This demonstrates the flexibility of Variants and Xojo’s ability to handle different data types.
Conversion of Floating-Point Numbers
In Xojo, assigning a floating-point number to a Variant will always produce a Double. However, there are other floating-point data types such as Single, Currency, and CGFloat.
Var dynamicValue As Variant = 3.14
Var myDouble As Double
Var mySingle As Single
Var myCurrency As Currency
Var myCGFloat As CGFloat
myDouble = dynamicValue // Double: 3.14
mySingle = dynamicValue // Single 3.14 (implicitly converted)
myCurrency = dynamicValue // Currency: 3.14 (implicitly converted)
myCGFloat = dynamicValue // CGFloat: 3.14 (implicitly converted)In this example, you can see that assigning dynamicValue (which contains a floating-point number) to different floating-point data types always works, with the implicit conversion performed by Xojo.
Advantages of Implicit Conversions
Flexibility
The biggest advantage of Variants is their flexibility. You can write functions that can work with different data types without requiring explicit type conversion.
Example of a Flexible Function
Function AddValues(value1 As Variant, value2 As Variant) As Variant
Return value1 + value2
End Function
// Using the function with different data types
Var result As Variant
result = AddValues(10, 20) // Integer addition
result = AddValues("Hello", " World") // String concatenation
result = AddValues(3.14, 2.71) // Double additionThis function can work with integers, strings, and doubles without requiring changes to the code.
Rapid Prototyping
During rapid prototyping, Variants can be useful because they reduce the need to worry about type conversions.
Example of a Quick Prototype
Var quickData As Variant = "42"
If quickData > 10 Then
MessageBox("Greater than 10")
End IfIn this example, the string “42” is automatically converted to an integer to perform the comparison.
Disadvantages of Implicit Conversions
Debugging
It can be difficult to debug errors caused by incorrect type conversions. Since the conversion happens automatically, it is sometimes not obvious why a particular error occurs.
Performance Issues
Implicit conversions can lead to performance issues, especially when large amounts of data need to be converted.
Example of Performance Issues
Var dynamicValue As Variant = "9999999999"
Var myDouble As Double
For i As Integer = 1 To 1000000
myDouble = dynamicValue // Performance hit due to repeated conversions
NextIn this example, the conversion is performed during each iteration of the loop, which can impact performance.
Loss of Type Safety
Another risk is the loss of type safety, which can lead to unexpected runtime errors.
Type Property
The Type property is a useful tool to determine the data type of a Variant value. This property returns an integer that corresponds to the type of the value. This can be helpful to ensure that you are handling the correct data type.
Example of Using the Type Property
Var dynamicValue As Variant = "Hello"
Select Case dynamicValue.Type
Case Variant.TypeString
MessageBox("The variant is a String.")
Case Variant.TypeInt32, _
Variant.TypeInt64
MessageBox("The variant is an Integer.")
Case Variant.TypeDouble
MessageBox("The variant is a Double.")
Case Variant.TypeBoolean
MessageBox("The variant is a Boolean.")
Else
MessageBox("The variant is of another type.")
End SelectIn this example, dynamicValue.Type is used to determine the type of the Variant value and perform corresponding actions.
When Should You Use Variants?
Suitable Use Cases
Generic Functions
If you are writing functions that need to work with different data types, Variants can be very useful.
Function CompareValues(value1 As Variant, value2 As Variant) As Boolean
Return value1 = value2
End Function
// Using the function with different data types
Var isEqual As Boolean
isEqual = CompareValues(10, 10) // True
isEqual = CompareValues("Hello", "Hello") // True
isEqual = CompareValues(3.14, 2.71) // FalseInteroperability with External APIs
When working with APIs or interfaces that return different data types, Variants can provide an easy way to handle this data.
// Example API response that can return different data types
Function GetApiResponse() As Variant
// Simulated API response
Return "42" // Could also be an Integer or a JSON object
End Function
Var apiResponse As Variant = GetApiResponse
If apiResponse.Type = Variant.TypeString Then
MessageBox("Response is a string: " + apiResponse)
ElseIf apiResponse.Type = Variant.TypeInt32 Or _
apiResponse.Type = Variant.TypeInt64 Then
MessageBox("Response is an integer: " + apiResponse)
End IfData Structures
In situations where you need data structures that contain different data types (e.g., an array that can contain both strings and numbers), Variants are a good choice.
Var dataList() As Variant
dataList.Add("Xojo")
dataList.Add(2024)
dataList.Add(True)
// Accessing different data types in the array
For Each item As Variant In dataList
Select Case item.Type
Case Variant.TypeString
MessageBox("String: " + item)
Case Variant.TypeInt32, _
Variant.TypeInt64
MessageBox("Integer: " + item)
Case Variant.TypeBoolean
MessageBox("Boolean: " + item)
End Select
NextSituations to Avoid Using Variants
Performance-Critical Applications
When performance is critical, you should avoid Variants because automatic type conversion introduces additional overhead.
Var dynamicValue As Variant = "9999999999"
Var myDouble As Double
For i As Integer = 1 To 1000000
myDouble = dynamicValue // Performance hit due to repeated conversions
NextCode Clarity and Maintainability
When code readability and maintainability are paramount, you should use explicit data types to ensure that the code is understandable to other developers.
Var myString As String = "Hello"
Var myInteger As Integer = 123
Function ConcatenateStrings(s1 As String, s2 As String) As String
Return s1 + s2
End Function
Var result As String
result = ConcatenateStrings(myString, myInteger.ToString) // Clear and understandableThe use of Variants in Xojo offers both advantages and disadvantages. While flexibility and rapid prototyping capabilities are compelling arguments, you should be aware of the potential problems that can arise from implicit conversions. Variants are best suited for scenarios where flexibility and generic programming are required. In performance-critical applications or projects that require high maintainability, it is advisable to use explicit data types such as String, Integer, Double, Boolean, Color etc. or, if you decide to use Variant, you can also have the explicit data type of the Variant delivered. To do this, use the Variant …Value properties (for example StringValue, IntegerValue, BooleanValue etc.).
By taking a conscious and deliberate approach to using Variants, you can leverage their advantages while avoiding potential pitfalls.
For more detailed information, you can refer to the official Xojo documentation on https://documentation.xojo.com/api/data_types/variant.html.
Martin T. is a Xojo MVP and has been very involved in testing Android support.