But this feature need not necessarily be in std::fmt. It could be a more general language feature, with a pluggable formatting policy, which would then help imp

But this feature need not necessarily be in std::fmt. It could be a more general language feature, with a pluggable formatting policy, which would then help improve the security of more specific libraries. That you shouldn't use unsafe string manipulation to do sensitive operations is obvious; the problem is that people do it anyway, which is why it is one of the most dangerous and common vulnerabilities.