4 ms·

Linear types are stronger than FnOnce, in that a linear type must be used _exactly_ once. Rust doesn't enforce that if you pass in a function of type FnOnce tha

Linear types are stronger than FnOnce, in that a linear type must be used _exactly_ once. Rust doesn't enforce that if you pass in a function of type FnOnce that it is called.

weavie 6y ago
Thats interesting. I don't quite understand how that would work. So can you work around that requirement by just going: if false then <use my type> else <do my things> Technically it is used exactly once, but really it will never be used..
- comex 6y ago
  That wouldn't work, because the value must be used in all possible control paths. In this case, both the 'then' and 'else' branch would have to use the value.
  - enlyth 6y ago
    Just curious, what is considered as 'using' the value?
    - anchpop 6y ago
      Passing it as a parameter to a function or returning it
      - waltpad 6y ago
        Or applying it if that value is a function. I believe the broader definition would be that it has to appear in an "evaluated" term.
- deleted 6y ago
  [deleted]
- maemre 6y ago
  Linear type systems often enforce that requirement by saying both branches need to use exactly the same linear values (or consume the same resources). So your example would be rejected by the type system. For example, the following function would not type check in a linearly-typed language because then branch is using x while else branch is not using x. -- Using Haskell-like syntax, '-o' is linear arrow, i.e. lollipop foo : Int -o Int -o Int foo x y = if y < 0 then x else 0