问题
I'm learning Rust and got to the chapter on trait bounds. In that chapter, they give an example with the + (plus) operator to enumerate all required traits in a where clause.
What other operators are allowed on traits in Rust? I searched but I wasn't able to find any documentation about this. Does Rust support 'or' notation, brackets, negation?
回答1:
'or' notation
No. Such a thing doesn't make sense to me — what would the code do if something could be A OR B?
brackets
No, unless you count the parenthesis in Fn(...) and friends, the use of angle brackets as generics (Vec<T>) or the use of square brackets in slices ([u8]), but these are parts of types.
Again, such a request doesn't make sense to me, why would you need any kind of grouping?
negation
No. I believe this is due to the fact that handling negative logic makes things a lot more complicated.
other operators
There's the ? (question mark) bound.
Source: I've written a parser of Rust code. While it's possible I've missed something, it parses all the ~37500 Rust files I've thrown at it, so it's a pretty good fit.
来源：https://stackoverflow.com/questions/46779310/what-are-the-possible-operators-for-traits-in-a-where-clause-in-rust