std::variant in C++ 17

C++17 has several valuable features that enhance the language's expressiveness and flexibility. The "std::variant", a powerful tool for handling variant types. Std::variant present in <variant> header, and it is a type-safe union that can store different time values. It represents a type-safe, stack-based, discriminated union. Unlike the traditional unions, which do not have type safety and exhibit undefined behaviour, std::variant ensures that the type of the stored value is always known at runtime, making it safer and more reliable.

The "std::variant" is useful where the value type may vary, and the code needs to adapt accordingly. It ensures that only one specified type can be stored at a given time.

How it is useful?

• Representing multiple possibilities: Models values that can have multiple, distinct states or representations.
• Alternatives to inheritance Representing multiple possibilities: Avoids hierarchies and virtual functions for representing variations.
• Visitor pattern implementation: Facilitates the visitor pattern for type-based operations.
• Error handling: Can represent potential errors or exceptional cases.
• State machines: Used to implement state machines effectively.

Example 1:

Let us take a simple program to illustrate the std::variant in C++.

Output:

Explanation:

In this program, the variant named myVariant is declared to hold values of different types: int, double, and string. So, three different values are assigned to the variant. First, the whole number 42 is assigned, then the decimal number is assigned, and a string is assigned. The program will print the types and values of the variant after each assignment. This variant feature allows a single variable to adapt to various data types, which provides a convenient and type-safe way to work with different scenarios in Cpp programming.

Example 2:

Let us take another simple program to illustrate the std::variant in C++.

Output:

Explanation:

The program demonstrates using std::variant to handle scenarios where a variable can represent different types. The program defines two custom data types: BatteryPoweredDevice and SolarPoweredDevice. The variant named deviceVariant is declared to hold either BatteryPoweredDevice or SolarPoweredDevice values. A BatteryPoweredDevice instance is assigned to deviceVariant with a specified battery voltage in the main function.

The program checks the active type within the variant using holds_alternative and then uses get to extract and print the relevant information. If the active type is BatteryPoweredDevice, it prints the battery voltage. If it's SolarPoweredDevice, it prints the solar panel efficiency. If the variant doesn't contain either of these types, it outputs a message indicating an unrecognized device type.

This example illustrates the flexibility of std::variant in handling variant types, which makes it a valuable tool for scenarios where the type of a variable can dynamically change. In this case, it simulates a system dealing with different types of powered devices, showcasing how std::variant provides a type-safe way to manage diverse data structures within a single variable.

Advantages:

• The "std::variant" ensures type-safety, eliminating the rist of runtime errors associated with traditional unions.
• It makes the code more readable and expressive.
• Type checking is performed at compile time, reducing the likelihood of runtime errors and improving overall code reliability.-3252
• It simplifies the handling of variant types.

Disadvantages

• The types that a std::variant can hold must be explicitly specified at compile time. This limitation may be restrictive in certain dynamic scenarios.
• Using std::variant can introduce some overhead in terms of increased code size and potentially slower compilation times.

Conclusion:

In conclusion, std::variant in C++17 is a powerful feature that enhances type safety and flexibility in handling variant types. It allows a single variable to adapt to different data types, making code more readable and expressive. While it introduces compile-time checks and simplifies the handling of variant types, it may have limitations in dynamic scenarios and can incur some overhead. Overall, std::variant is a valuable tool for managing diverse data structures within a single variable, offering a safer and more efficient approach to handling variant types in C++.