"Const" is confusing

[jruderman]

In Rust, const means several things:

• const items (document const items #3341)
• The const kind (Add deep const kind #2421), which represents deep immutability
• const pointers, which can point to mutable or immutable data, but cannot be used to mutate it

I think const pointers are the most confusing and should be renamed to something else (perhaps read pointers). This confusion may have contributed to the unsoundness fixed in 5d540de#L7L1206

[catamorphism]

I also think const is confusing (I'm not a C++ programmer, and expect it to mean "constant"). I'm in favor of changing it to something less confusing.

[nikomatsakis]

I agree. I think using const to mean both immutable and read-only is asking for confusion. The distinction is subtle as it is. I'd be happy with most anything. Maybe even &mut? T. :)

[brson]

Will we still need const pointers when vector interiors can no longer be explicitly mutable?

[bblum]

I believe const pointers are still an important part of borrowck. AIUI, if you write a function that takes a &T, purity gets involved if you want to call it when what you have is a &mut T. But if the function can be written to take a &const T, it can be called more easily / in more cases(?).

Maybe the thing it makes most sense to rename is const-the-kind, the one that means "no mutable fields inside". It is kind of like send/owned in that regard ("The type structure does not have this thing inside it").

[graydon]

At this point I believe we're down to just the kind/trait; closing as fixed-ish. Reopen if you feel it's still confusing.