Can std::string Be Used in Constant Expressions in C 20 and Beyond?

Constant Expressions and std::string: A Journey to C 20

Originally, the question posed a dilemma in using std::string in constant expressions, deeming it impossible due to a non-trivial destructor. However, the landscape has evolved with the introduction of C 20.

In C 20, std::string can indeed be employed in constant expressions, provided that it is destroyed by the end of constant evaluation. This allows for expressions like:

constexpr std::size_t n = std::string("hello, world").size();

This is because the temporary std::string object created in the expression is destroyed before the constant expression evaluation completes.

However, an alternative and more robust approach for C 17 and later is to use std::string_view, which is explicitly designed for use in constant expressions:

constexpr std::string_view sv = "hello, world";

std::string_view is a string-like object that provides an immutable, non-owning reference to a character sequence. It offers the functionality of a std::string without incurring the overhead of owning the underlying data.

In summary, while std::string can be used in constant expressions with C 20's relaxation of restrictions, std::string_view remains the preferred choice for constant expression handling in C 17 and beyond, ensuring immutability and memory efficiency.

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