Quick Q: Is constexpr more constant than const? -- StackOverflow

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Is a constexpr more “constant” than const?

The C++ Programming Language Fourth Edition - Bjarne Stroustrup: (emphasis mine)

2.2.3. Constants

In a few places, constant expressions are required by language rules (e.g., array bounds (§2.2.5, §7.3), case labels (§2.2.4, §9.4.2), some template arguments (§25.2), and constants declared using constexpr). In other cases, compile-time evaluation is important for performance. Independently of performance issues, the notion of immutability (of an object with an unchangeable state) is an important design concern (§10.4).

It seems that Stroustrup is suggesting here that constexpr ensures immutability of an object better than a traditional const declaration. Is this correct? Are there ways in which constexpr can be more secure/less volatile than const, or does Stroustrup simply mean that since there are ways to use constexpr that are not supported with const (see Is constexpr really needed?), in those cases immutability can be ensured using constexpr?


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