What's the difference of the module core and std? Thanks
core should be self-contained.
std depends on
core, and a lot of other stuff, to provide a kind of "facade" to the end user.
Thank you very much for your answer. Is "self-contained" means that it just like java.lang package? Sorry, my English is very pool, I hope you can understand it.
"self-contained" means that it does not depend on anything outside of itself, not even on allocations. This means it is suitable to work with even when implementing e.g. operating systems, where you cannot depend on things like allocation (because that requires a virtual memory model that your system needs to build first before it can build on it).
For most end users, the distinction doesn't matter; just use