Learning Guide: Casting and Type Conversion in C#

Introduction to Casting and Type Conversion

Casting and type conversion are fundamental concepts in programming that allow you to manipulate and convert data of one type to another in C#. Type conversion ensures that data is correctly interpreted and used by the program, enabling smooth interoperability between different data types.

This learning guide will cover various aspects of casting and type conversion in C#, including implicit and explicit casting, type conversion methods, and common scenarios where type conversion is necessary.

Table of Contents

1. Understanding Data Types

   • Primitives vs. Reference Types
   • Value Types vs. Reference Types

2. Implicit Casting

   • Casting between Compatible Types
   • Widening Conversions

3. Explicit Casting

   • Casting between Incompatible Types
   • Narrowing Conversions
   • Handling Potential Data Loss

4. Type Conversion Methods

   • Convert Class
   • Parse and TryParse Methods
   • ToString and ToString Overloads

5. User-Defined Type Conversion

   • Implementing Implicit and Explicit Operators
   • Converting Custom Types

6. Handling Type Conversion Errors

   • Handling Invalid Cast Exceptions
   • Using Try-Catch Blocks

7. Casting and Type Conversion Best Practices

   • Avoiding Unnecessary Conversions
   • Choosing the Right Conversion Method
   • Minimizing Data Loss

8. Common Scenarios for Type Conversion

   • Converting Numbers to Strings and Vice Versa
   • Converting Enums
   • Converting between DateTime and String

9. Advanced Topics

   • Type Conversion with Generics
   • Type Conversion in LINQ Queries

10. Exercises and Coding Challenges

    • Implementing Custom Type Conversions
    • Converting Between Measurement Units
    • Handling Type Conversion in Real-world Scenarios

11. Summary and Conclusion

    • Recap of Key Concepts
    • Importance of Type Safety and Data Integrity

Learning Objectives

By the end of this learning guide, learners should be able to:

• Differentiate between value types and reference types in C#.
• Perform implicit and explicit casting between compatible and incompatible types.
• Utilize type conversion methods like Convert, Parse, and ToString.
• Implement user-defined type conversions using implicit and explicit operators.
• Handle potential type conversion errors using try-catch blocks.
• Apply best practices for efficient and safe type conversion.
• Solve common programming scenarios involving type conversion.

Prerequisites

To make the most of this learning guide, you should have a basic understanding of C# syntax and programming concepts. Familiarity with variables, data types, and basic control structures will be beneficial.

Let's dive into the world of casting and type conversion in C# and enhance your programming skills!

Understanding Data Types

In programming, data types define the kind of data that a variable can hold and the operations that can be performed on that data. C# provides various built-in data types, which can be broadly categorized into two main groups: primitives (also known as simple types) and reference types.

Primitives vs. Reference Types

Primitives (Simple Types): Primitives are basic data types that store simple values. They are value types, meaning they directly store the value in memory. Common primitive types in C# include:

• int: Represents integers (whole numbers).
• double: Represents floating-point numbers with double precision.
• char: Represents a single Unicode character.
• bool: Represents a Boolean value (true or false).

Primitives are efficient in terms of memory usage and performance because the actual value is stored directly in the memory location allocated for the variable.

Reference Types: Reference types, on the other hand, store references to objects in memory rather than the actual value. They include objects, arrays, strings, and custom classes. Common reference types in C# are:

• Objects (instances of classes)
• Arrays
• Strings
• Custom classes and structures

Reference types store a memory address pointing to the location where the actual data is stored. This allows for more complex data structures and sharing data between variables.

Value Types vs. Reference Types

Value Types: Value types directly store the data in the memory allocated for the variable. When you assign a value type variable to another variable, a copy of the value is made. Changes in one variable do not affect the other. Examples of value types include integers, floating-point numbers, and characters. Value types are stored on the stack.

Reference Types: Reference types store references to the data in memory. When you assign a reference type variable to another variable, both variables refer to the same data in memory. Changes to the data through one variable are reflected in the other. Examples of reference types include objects, arrays, and strings. Reference types are stored on the heap.

Understanding the distinction between primitives and reference types, as well as value types and reference types, is crucial for effective memory management, avoiding unintended side effects, and making informed decisions about type conversions.

In the following sections of this learning guide, we will explore how to perform casting and type conversion between these different types, enabling you to work with diverse data types seamlessly in C#.

Implicit Casting

Implicit casting, also known as implicit conversion, is the process of converting a value of one data type to another data type automatically by the compiler. Implicit casting is allowed when there is no risk of data loss or loss of precision, and the target data type can accommodate the source data type without any issues.

Casting between Compatible Types

When casting between compatible types, such as from a smaller data type to a larger one, C# automatically performs the conversion without requiring any explicit syntax from the programmer. For example, consider the following implicit casting scenarios:

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int integerValue = 42;
double doubleValue = integerValue; // Implicit casting from int to double

In this example, the integerValue of type int is implicitly cast to a doubleValue of type double. Since double can hold larger values than int, no data loss occurs, and the conversion is safe.

Widening Conversions

Implicit casting that results in increasing the size or precision of the data type is called a widening conversion. Widening conversions are generally safe because they don't lead to data loss. Here are a few examples of widening conversions:

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float floatValue = 3.14f;
double doubleValue = floatValue; // Implicit casting from float to double

short shortValue = 100;
int intValue = shortValue; // Implicit casting from short to int

In the first example, the floatValue of type float is implicitly cast to a doubleValue of type double. In the second example, the shortValue of type short is implicitly cast to an intValue of type int. Both conversions involve widening the data types, so there's no risk of losing information.

It's important to note that not all conversions are implicitly allowed. When casting between incompatible or potentially lossy conversions, explicit casting or conversion methods are required.

Implicit casting is a powerful feature that simplifies code and improves readability. However, it's crucial to be aware of the type conversions taking place to avoid unexpected results or data loss.

Explicit Casting

Explicit casting, also known as explicit conversion, is the process of manually converting a value from one data type to another data type that is not directly compatible. Unlike implicit casting, explicit casting requires the programmer to provide explicit instructions to the compiler for the conversion.

Casting between Incompatible Types

Explicit casting is necessary when converting between data types that might result in data loss or when converting from a larger data type to a smaller one. Since these conversions can lead to loss of information or precision, C# requires the programmer to explicitly indicate their intention to perform the conversion.

Narrowing Conversions

When converting from a larger data type to a smaller data type, it's possible to lose information, which is why explicit casting is required. This type of conversion is called a narrowing conversion. For example:

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double doubleValue = 3.14;
int integerValue = (int)doubleValue; // Explicit casting from double to int

In this example, the doubleValue of type double is explicitly cast to an integerValue of type int. Since int cannot hold decimal places, the fractional part of the doubleValue is lost during the conversion.

Handling Potential Data Loss

To perform explicit casting, you need to enclose the target data type in parentheses and place it before the value you're converting. While explicit casting can be useful, you should exercise caution to avoid unexpected results or data loss. Always consider the range and precision of the target data type before performing explicit casting.

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double bigValue = 123456789.99;
int intValue = (int)bigValue; // intValue will be 123456789

In this case, the fractional part of bigValue is lost during the explicit casting, resulting in a truncated integer value.

When performing explicit casting, it's also a good practice to use exception handling to catch potential errors that might arise due to invalid conversions. The InvalidCastException can occur if the conversion cannot be performed.

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try
{
    double invalidValue = 12.34;
    int invalidInt = (int)invalidValue; // Explicit casting can throw InvalidCastException
}
catch (InvalidCastException ex)
{
    Console.WriteLine("Invalid casting: " + ex.Message);
}

Explicit casting allows you to take control over conversions that could result in data loss or unintended consequences. It's essential to be mindful of the limitations of the target data type and potential loss of information when performing explicit casting.

Type Conversion Methods

In addition to implicit and explicit casting, C# provides several built-in methods and techniques for performing type conversion. These methods offer greater flexibility and control over the conversion process, especially when dealing with more complex scenarios or user input.

Convert Class

The Convert class in C# provides static methods that allow you to convert values between different data types. It offers various methods for converting numeric types, strings, dates, and more. Some common methods include:

• Convert.ToInt32(): Converts a value to an integer.
• Convert.ToDouble(): Converts a value to a double.
• Convert.ToString(): Converts a value to a string.

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int integerValue = Convert.ToInt32("42");
double doubleValue = Convert.ToDouble("3.14");

The Convert class handles conversion exceptions gracefully by returning default values or throwing an exception if the conversion is not possible.

Parse and TryParse Methods

For converting strings to other data types, C# provides Parse and TryParse methods for many built-in types. These methods are particularly useful when dealing with user input or reading data from files.

• int.Parse(), double.Parse(), etc.: Converts a string to the specified numeric type.
• bool.Parse(): Converts a string to a boolean value.

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string numericString = "123";
int parsedInt = int.Parse(numericString);

TryParse methods are safer to use when dealing with user input since they don't throw exceptions if the conversion fails. Instead, they return a Boolean indicating whether the conversion was successful and an output parameter to hold the converted value.

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string userInput = "abc";
bool isConversionSuccessful = int.TryParse(userInput, out int result);
if (isConversionSuccessful)
{
    Console.WriteLine("Conversion successful. Result: " + result);
}
else
{
    Console.WriteLine("Conversion failed.");
}

ToString and ToString Overloads

The ToString() method is available on all objects in C# and allows you to convert an object to its string representation. This is especially useful when you want to concatenate different data types within a string or display data.

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int integerValue = 42;
string stringValue = integerValue.ToString();

Many data types also provide overloads for the ToString() method that allow you to customize the format of the string representation. For example, the ToString("C") overload formats a numeric value as currency.

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double currencyValue = 123.45;
string formattedCurrency = currencyValue.ToString("C");

Type conversion methods offer a powerful way to handle conversions between various data types, especially when dealing with strings or complex scenarios. They provide more control over error handling and allow you to format data as needed for your application's requirements.

User-Defined Type Conversion

In addition to the built-in type conversion mechanisms, C# allows you to define your own type conversions for custom classes and structures. This is useful when you want to provide a seamless way to convert between instances of your custom types and other existing data types.

Implementing Implicit and Explicit Operators

C# provides two types of user-defined type conversion operators: implicit and explicit. These operators allow you to define how instances of your custom type can be implicitly or explicitly converted to other data types.

• Implicit Conversion Operator (implicit): This operator allows for automatic conversion without any explicit cast. Implicit operators are used when there's no risk of data loss or loss of precision.

• Explicit Conversion Operator (explicit): This operator requires an explicit cast in code. Explicit operators are used when there's a possibility of data loss or when you want to make sure the programmer is aware of the conversion.

Here's an example of implementing both implicit and explicit conversion operators for a custom class:

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public class Distance
{
    public double Meters { get; }

    public Distance(double meters)
    {
        Meters = meters;
    }

    // Implicit operator for converting from Distance to double
    public static implicit operator double(Distance distance)
    {
        return distance.Meters;
    }

    // Explicit operator for converting from double to Distance
    public static explicit operator Distance(double meters)
    {
        return new Distance(meters);
    }
}

With the above class definition, you can perform conversions as follows:

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Distance distance = new Distance(1000);
double meters = distance; // Implicit conversion

double value = 2000;
Distance newDistance = (Distance)value; // Explicit conversion

Converting Custom Types

When defining your own custom types, you have control over how they are converted to and from other types. This enables you to create more intuitive and convenient APIs for your classes, making them easier to work with in different contexts.

For instance, if you have a custom Temperature class:

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public class Temperature
{
    public double Celsius { get; }

    public Temperature(double celsius)
    {
        Celsius = celsius;
    }
}

You can implement custom conversion methods or operators to convert temperatures between Celsius and Fahrenheit:

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public static class TemperatureConverter
{
    public static Temperature FromFahrenheit(double fahrenheit)
    {
        return new Temperature((fahrenheit - 32) * 5 / 9);
    }

    public static double ToFahrenheit(Temperature temperature)
    {
        return temperature.Celsius * 9 / 5 + 32;
    }
}

With these methods, you can easily convert temperatures:

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Temperature celsiusTemp = new Temperature(25);
double fahrenheitValue = TemperatureConverter.ToFahrenheit(celsiusTemp);

Temperature newCelsiusTemp = TemperatureConverter.FromFahrenheit(77);

User-defined type conversion provides a way to create more intuitive and expressive APIs for your custom classes, allowing users of your code to work with your types in a more natural and seamless manner.

Handling Type Conversion Errors

When performing type conversions, especially explicit conversions, there's a possibility of encountering errors. These errors can lead to exceptions being thrown, disrupting the normal flow of your program. It's important to handle these exceptions gracefully to ensure your program remains robust and doesn't crash unexpectedly.

Handling Invalid Cast Exceptions

One common exception that can occur during type conversion is the InvalidCastException. This exception is thrown when an explicit cast between incompatible types is attempted. For example:

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try
{
    int integerValue = 42;
    object objValue = integerValue;

    string stringValue = (string)objValue; // InvalidCastException
}
catch (InvalidCastException ex)
{
    Console.WriteLine("Invalid cast: " + ex.Message);
}

To avoid such exceptions, you can use type-checking before performing the conversion or use safer methods like as and is to handle conversions without throwing exceptions.

Using Try-Catch Blocks

To handle type conversion errors effectively, you can use try-catch blocks to catch exceptions and respond appropriately. Here's an example:

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try
{
    int integerValue = 42;
    object objValue = integerValue;

    string stringValue = (string)objValue; // InvalidCastException will be caught
    Console.WriteLine("Conversion successful. String value: " + stringValue);
}
catch (InvalidCastException ex)
{
    Console.WriteLine("Invalid cast: " + ex.Message);
}
catch (Exception ex)
{
    Console.WriteLine("An unexpected error occurred: " + ex.Message);
}

In this example, a try-catch block catches the InvalidCastException if the conversion fails. It's a good practice to handle more specific exceptions before handling the broader Exception base class. This way, you can provide specific error messages or actions for different types of errors.

Remember that while try-catch blocks can handle exceptions, it's even better to design your code in a way that minimizes the chances of exceptions occurring in the first place. You can use techniques like type-checking or utilizing safer conversion methods like TryParse to prevent exceptions from being thrown.

Casting and Type Conversion Best Practices

Casting and type conversion are important tools in programming, but it's crucial to use them wisely to ensure your code is efficient, maintainable, and error-free. Here are some best practices to keep in mind:

Avoiding Unnecessary Conversions

1. Use the Appropriate Data Type: Choose the most appropriate data type for your variables to begin with, so you don't need unnecessary conversions later.

2. Avoid Redundant Conversions: Avoid converting between types unnecessarily, as it can lead to code clutter and potential performance overhead.

Choosing the Right Conversion Method

1. Use Implicit Conversion When Possible: Whenever possible, rely on implicit conversion, especially for widening conversions. It simplifies your code and makes it more readable.

2. Prefer Built-in Conversion Methods: Utilize built-in conversion methods like Convert, Parse, and TryParse when working with standard types.

3. Use User-Defined Conversion for Custom Types: Implement user-defined conversion operators only when they provide meaningful and intuitive behavior for your custom types.

Minimizing Data Loss

1. Be Aware of Data Loss: Always be aware of potential data loss when performing conversions, especially from larger to smaller types.

2. Use Explicit Conversion for Data Loss: If data loss is expected, use explicit conversion operators or methods. This signals to other programmers that there might be a loss of information.

3. Handle Data Loss Gracefully: When data loss can occur, handle it gracefully by validating input or providing appropriate error messages.

Validation and Error Handling

1. Use Try-Catch Blocks: Wrap explicit conversions in try-catch blocks to handle potential exceptions.

2. Use TryParse for User Input: When working with user input, use TryParse methods to avoid throwing exceptions due to invalid input.

3. Check for Invalid Casts: Use the as keyword and the is keyword to check for compatibility before performing explicit casting.

Testing and Validation

1. Test Different Scenarios: Test your type conversion code with various scenarios, including edge cases and unexpected inputs.

2. Unit Testing: Write unit tests to ensure that your type conversion methods behave as expected and handle different cases correctly.

3. Validation in Real-world Context: Consider the context in which your program will be used. Ensure that your type conversions work correctly and intuitively in the specific application domain.

By following these best practices, you can effectively use casting and type conversion in your C# programs to improve code quality, prevent errors, and create more reliable and maintainable software.

Common Scenarios for Type Conversion

Converting Numbers to Strings and Vice Versa

Converting between numeric types and strings is a common task in programming. You might need to convert numbers to strings for display purposes or read numeric values from user input in string format.

Converting Numbers to Strings:

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int integerValue = 42;
string stringValue = integerValue.ToString(); // Convert int to string

Converting Strings to Numbers:

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string numericString = "123";
int parsedInt = int.Parse(numericString); // Convert string to int

Using int.TryParse() is recommended when converting strings to numbers to handle cases where the string might not represent a valid number.

Converting Enums

Enums are a powerful way to represent a set of named constant values. Converting enums to and from their underlying integral values is often required, especially when interacting with external data or APIs.

Converting Enum to Integral Value:

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enum Days { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday }
int dayValue = (int)Days.Wednesday; // Convert enum to int

Converting Integral Value to Enum:

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int intValue = 3;
Days day = (Days)intValue; // Convert int to enum

Ensure that the integral value you're converting from is a valid value for the enum to avoid unexpected behavior.

Converting between DateTime and String

Working with dates and times often involves converting DateTime instances to string representations and vice versa.

Converting DateTime to String:

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DateTime currentDate = DateTime.Now;
string dateString = currentDate.ToString("yyyy-MM-dd"); // Convert DateTime to string

Converting String to DateTime:

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string dateInput = "2023-08-09";
DateTime parsedDate = DateTime.ParseExact(dateInput, "yyyy-MM-dd", CultureInfo.InvariantCulture); // Convert string to DateTime

Using DateTime.TryParseExact() is safer when converting strings to DateTime, as it allows you to specify the exact format expected and handles invalid inputs more gracefully.

These common scenarios highlight the practicality of type conversion in various programming tasks. Understanding and mastering these conversion techniques will allow you to work effectively with different data types and improve the functionality of your applications.

Advanced Topics in Type Conversion

Type Conversion with Generics

Generics provide a way to write flexible and reusable code that works with different data types. Type conversion can also be applied within generic classes and methods to handle a wide range of data types.

For instance, you can create a generic method that converts a value to a specific type:

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public T ConvertValue<T>(object value)
{
    return (T)Convert.ChangeType(value, typeof(T));
}

Here, the Convert.ChangeType() method handles the actual conversion. You can use this method to convert various types:

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int intValue = ConvertValue<int>("42");
double doubleValue = ConvertValue<double>("3.14");

Type Conversion in LINQ Queries

Language Integrated Query (LINQ) allows you to query collections using a SQL-like syntax. Type conversion can play a role in LINQ queries when you're working with different data types in your data source.

For example, consider a LINQ query that filters and projects data:

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List<string> words = new List<string> { "apple", "banana", "cherry" };

IEnumerable<int> wordLengths = words
    .Where(word => word.Length > 5)
    .Select(word => word.Length);

In this case, the Select() method projects the lengths of words as int values, automatically performing type conversion from int to string in the process.

Type conversion can also be useful when working with custom objects:

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public class Product
{
    public string Name { get; set; }
    public double Price { get; set; }
}

List<Product> products = new List<Product>
{
    new Product { Name = "Apple", Price = 1.0 },
    new Product { Name = "Banana", Price = 0.75 },
    new Product { Name = "Cherry", Price = 2.5 }
};

IEnumerable<string> productNames = products
    .Where(product => product.Price > 1.0)
    .Select(product => product.Name);

In LINQ queries, type conversion can occur implicitly or explicitly based on the projection and filtering operations you perform.

Understanding how type conversion works within generics and LINQ queries can help you write more versatile and efficient code when dealing with diverse data types and complex queries.

Exercises and Coding Challenges

Implementing Custom Type Conversions

Exercise: Create a custom class Temperature that represents temperatures in both Celsius and Fahrenheit. Implement implicit and explicit operators to convert between Celsius and Fahrenheit temperatures. Test the conversions using various temperature values.

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public class Temperature
{
    public double Celsius { get; }

    public Temperature(double celsius)
    {
        Celsius = celsius;
    }

    public static implicit operator Temperature(double celsius)
    {
        return new Temperature(celsius);
    }

    public static explicit operator double(Temperature temperature)
    {
        return temperature.Celsius;
    }

    public static implicit operator Temperature(Fahrenheit fahrenheit)
    {
        return new Temperature((fahrenheit.Value - 32) * 5 / 9);
    }
}

public class Fahrenheit
{
    public double Value { get; }

    public Fahrenheit(double value)
    {
        Value = value;
    }
}

Converting Between Measurement Units

Challenge: Implement a class LengthConverter that allows conversion between different length measurement units such as inches, centimeters, feet, and meters. Provide methods to convert from one unit to another using appropriate conversion factors.

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public class LengthConverter
{
    public double InchesToCentimeters(double inches)
    {
        return inches * 2.54;
    }

    public double CentimetersToInches(double centimeters)
    {
        return centimeters / 2.54;
    }

    // Implement similar methods for other conversions
}

Handling Type Conversion in Real-world Scenarios

Scenario: Imagine you're building a currency converter application. You receive currency exchange rates as strings and need to convert between different currencies accurately.

Challenge: Implement a function that takes an amount in one currency, the exchange rate, and the target currency. Convert the amount to the target currency and return the result as a string. Handle invalid input and potential errors gracefully.

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public class CurrencyConverter
{
    public string ConvertCurrency(string amount, string exchangeRate, string targetCurrency)
    {
        if (decimal.TryParse(amount, out decimal amountValue) &&
            decimal.TryParse(exchangeRate, out decimal rateValue))
        {
            decimal convertedAmount = amountValue * rateValue;
            return $"{convertedAmount} {targetCurrency}";
        }
        else
        {
            return "Invalid input";
        }
    }
}

In these exercises and challenges, you'll practice implementing custom type conversions, working with real-world scenarios involving type conversion, and applying your knowledge to solve practical problems. This will help reinforce your understanding of type conversion concepts and their application in various contexts.