Introduction
Map literals are a convenient way to define and initialize maps in programming languages. Unfortunately, C++ does not have built-in support for map literals like some other languages such as Python or JavaScript. However, with a little bit of ingenuity, we can create our own custom map literals in C++. This blog post will demonstrate how to define and use custom map literals in C++.
Using Structured Bindings
C++ introduced structured bindings in the C++17 standard, which allow us to destructure objects into their individual components. We can leverage structured bindings to create a syntax that resembles map literals.
To define our custom map literal, we will create a template function make_map that takes a list of key-value pairs and returns a map. Each key-value pair is provided as a tuple.
#include <map>
#include <tuple>
template <typename... T>
auto make_map(T&&... pairs) {
return std::map{std::make_pair(std::forward<T>(pairs))...};
}
Example Usage
Let’s see an example of how to use our custom map literal.
#include <iostream>
int main() {
auto my_map = make_map(
std::make_pair("key1", 42),
std::make_pair("key2", "value"),
std::make_pair("key3", 3.14)
);
for (const auto& [key, value] : my_map) {
std::cout << key << ": " << value << std::endl;
}
return 0;
}
The make_map function is used to initialize my_map with key-value pairs. We can then iterate over the map using a structured binding to print each key-value pair.
Limitations
It’s important to note that custom map literals in C++ have some limitations compared to native map literals in other languages. For instance, the key-value pairs must be provided as explicit std::make_pair calls, and the types of the keys and values must be explicitly specified.
Conclusion
While C++ does not have built-in map literals, we can create our own custom map literals using structured bindings. By defining a template function make_map, we can initialize maps with a syntax that resembles map literals in other programming languages. Although there are limitations, this technique can be useful in making the code more concise and readable while working with maps in C++.
Useful References:
#cpp #custommapliterals