Custom boolean literals in C++

23 Oct 2023

References

Boolean literals in C++ have fixed values, true and false, which represent the two possible states of a boolean variable. However, with user-defined literals, C++ allows us to define our own custom literals, including boolean literals, with custom semantics. In this blog post, we will explore how we can create custom boolean literals in C++.

What are User-Defined Literals?

User-defined literals are a feature introduced in C++11 that allows programmers to define their own literal suffixes. These suffixes can be attached to numeric, string, or boolean literals, and are used to extend the language with custom types and operations.

Defining Custom Boolean Literals

To define a custom boolean literal, we use the “operator”” followed by the desired suffix. Let’s say we want to define a custom boolean literal suffix "_yes" that represents true, and "_no" that represents false. We can achieve this by overloading the operator"" for our suffixes as follows:

constexpr bool operator"" _yes(const char*) {
    return true;
}

constexpr bool operator"" _no(const char*) {
    return false;
}

In the above code, the operator"" _yes and operator"" _no are user-defined literal operators for our custom suffixes "_yes" and "_no", respectively. These operators take a const char* parameter, which contains the string literal, and return a boolean value.

Using Custom Boolean Literals

Once we have defined our custom boolean literals, we can use them just like any other boolean literals in our code. Here’s an example:

#include <iostream>

void print_bool(bool value) {
    std::cout << (value ? "Yes" : "No") << std::endl;
}

int main() {
    bool result = true_yes;
    print_bool(result); // Output: Yes
    
    bool flag = false_no;
    print_bool(flag); // Output: No
    
    return 0;
}

In the above example, we define a function print_bool that takes a boolean value and prints “Yes” if the value is true, and “No” if the value is false. We then use our custom boolean literals, true_yes and false_no, to demonstrate their usage.

Benefits of Custom Boolean Literals

Using custom boolean literals can provide several benefits in C++ code.

One possible use case could be in expressing boolean conditions in a more readable and intuitive way. For example, instead of writing if (status == 1) or if (status == true), we can use a custom boolean literal like if (status_yes) to make the condition more expressive and self-explanatory.

Another benefit is the ability to define boolean literals that match the domain-specific language (DSL) of your code. This can improve code readability and make it easier to understand by other developers working on the same project.

Conclusion

In this blog post, we explored how to create custom boolean literals in C++. We learned that by using user-defined literals, we can define our own custom boolean literal suffixes with the desired semantics. This feature allows us to make our code more expressive and easier to understand. With the ability to define boolean literals matching our domain-specific language, we can write more readable code and improve collaboration among team members.

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