tagged

Memory is tagged as code or data during load time with all input from I/O tagged as data by default by hardware.

It's almost right, but it would be much easier to follow the conversation if each comment was tagged with the story it refers to.

If input is tagged by the developer, what's to stop the developer from forgetting to tag the input correctly?

Strings are a good example of this: short strings can be tagged pointers, and long strings can be dynamically allocated.

Pointers are tagged for protection, actual value inaccessible by apps, and created by program loader only.

C++ (like C) has union, with which you can build tagged unions (aka sum types).

Unfortunately this isn't an option in Objective-C because the compiler can't make any assumptions about the tagged pointer implementation, and that means objc_msgSend has to start fresh at each invocation.

Anyone able to do so would be able to source the other server and therefore replicate the tagged data that it chooses to cache.

As another commenter mentioned, some C++ implementations use tagged pointers for std::string.

They also use tagged pointers, but it is a single bit outside of what the apps can see, and marks a pointer as modified.

The other way round (deciding whether a newly minted string of length 10 can be put in a tagged pointer) is slightly more complex.

Of course, more often they're boiling political agendas down to 140 characters, or worse, splitting a page-length message up into 17 chunks tagged (1/17).

Just get in on Google's dime and join the latest hot startup next week after they've tagged "H1B" on their passport.

I expect the string "née" would become a tagged pointer string, for example.

Tagged pointers really have nothing to do with late binding.

Tagged/capability CPU's, better architectures for OS's, compilers that automatically enforce strong safety/security, static analysis tools that prove absence of common bugs, type systems for high level languages easy to code in...