How is "const correctness" related to ordinary type safety?, C++ FAQ

C++ FAQ / Section 18 / FAQ 18.2

Section 18:

18.1	What is "`const` correctness"?
18.2	How is "`const` correctness" related to ordinary type safety?
18.3	Should I try to get things `const` correct "sooner" or "later"?
18.4	What does "`Fred const* p`" mean?
18.5	Difference between "`Fred const* p`", "`Fred* const p`" and "`Fred const* const p`"?
18.6	What does "`Fred const& x`" mean?
18.7	Does "`Fred& const x`" make any sense?
18.8	What does "`const X& x`" mean?
18.9	What does "`const X* x`" mean?
18.10	What is a "`const` member function"?
18.11	Using return-by-reference in a `const` member function?
18.12	What's the deal with "`const`-overloading"?
18.13	How a `const` member function can make an "invisible" change to a data member?
18.14	Does `const_cast` mean lost optimization opportunities?
18.15	Binding a pointer-to-`const` to a non-`const` object?
18.16	Does "`Fred const* p`" mean that `*p` can't change?
18.17	Errors trying to convert `Foo` → `Foo const`?

[18.2] How is "const correctness" related to ordinary type safety?

Declaring the const-ness of a parameter is just another form of type safety. It is almost as if a const std::string, for example, is a different class than an ordinary std::string, since the const variant is missing the various mutative operations in the non-const variant (e.g., you can imagine that a const std::string simply doesn't have an assignment operator).

If you find ordinary type safety helps you get systems correct (it does; especially in large systems), you'll find const correctness helps also.