Custom URL literals in C++

23 Oct 2023

In modern C++, we have the ability to create custom user-defined literals (UDLs) to extend the language’s syntax and make code more expressive. This feature allows us to create our own literal suffixes for different data types, such as strings, numbers, and now even URLs!

URLs are commonly used in web development and networking. With custom URL literals, we can easily represent and manipulate URLs in a more intuitive way.

Let’s see how we can define and use custom URL literals in C++.

Defining Custom URL Literals

To define a custom URL literal, we need to define an operator function that is responsible for converting the literal expression into the desired data type, in this case, a URL object.

Here’s an example of a custom URL literal operator function:

#include <iostream>
#include <string>

class URL {
public:
    URL(const std::string& url) : url(url) {}

    void print() {
        std::cout << "URL: " << url << std::endl;
    }

private:
    std::string url;
};

URL operator"" _url(const char* str, size_t) {
    return URL(str);
}

In this example, we define a URL class to represent URLs and a corresponding operator"" _url function that takes a string literal and converts it into a URL object.

Using Custom URL Literals

Once we have defined the custom URL literal operator, we can use it in our code. Here’s an example of how we can create and use URL objects using the custom URL literal:

int main() {
    URL url = "https://example.com"_url;
    url.print();
    
    return 0;
}

In this example, we create a URL object by directly assigning the URL string literal to it, followed by the _url literal suffix. This allows us to create a URL object more naturally and concisely.

Benefits of Custom URL Literals

Custom URL literals provide several benefits:

Readability: Custom literals make code more readable and self-explanatory. Using a custom URL literal makes it clear that the assigned value is intended to represent a URL.
Type safety: By defining a custom literal operator, we can enforce type safety and ensure that only valid URLs are created using the literal.
Expressiveness: Custom literals allow us to express our intentions more directly. Instead of passing a regular string to represent a URL, we can use a custom literal to indicate its purpose explicitly.

Conclusion

Custom URL literals in C++ allow us to extend the language’s syntax and make code more expressive when working with URLs. By defining a custom literal operator, we can create and manipulate URLs in a more natural and intuitive way.

Using custom literals not only improves code readability but also enhances type safety and expresses our intentions more clearly.

Try incorporating custom URL literals in your C++ code to make the manipulation of URLs more elegant and intuitive!

References:
[1] C++ Reference - User-defined literals: https://en.cppreference.com/w/cpp/language/user_literal
[2] C++20 Standard Proposal for URL Literals: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0846r2.pdf

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