Overview

Proxy type	Lifetime	Concurrency considerations / Notes
cref	Observed object must outlive call. Constructed with [[msvc/clang::lifetimebound]]	Threadsafe, if observed object self is const during lifetime of observer.
mutref	Observed object must outlive call. Constructed with [[msvc/clang::lifetimebound]]	Not threadsafe.
shared	Same as std::shared_ptr< const>.	Threadsafe.
unique	Same as std::unique_ptr	Threadsafe.
value	Same as std::any	Threadsafe.

Lifetime castability

v-to\from->	cref	mutref	shared	unique	val
cref	yes	yes	yes	yes	yes
mutref	no	yes	no	yes	yes
shared	no	no	yes	no	no
unique	no	no	no	no	no
value	no	no	yes	no	no

v-to\from->	cref	mutref	shared	unique	val
cref	yes	yes	no	no	no
mutref	no	yes	no	no	yes
shared	no	no	yes	yes	yes
unique	no	no	no	no	no
value	no	no	TODO	TODO	yes

v-to\from->	cref	mutref	shared	unique	val
cref	no	no	no	no	no
mutref	no	no	no	no	no
shared	yes	yes	yes	yes	yes
unique	yes	yes	yes	yes	yes
value	yes	yes	yes	yes	yes