vstd::tokens::frac

Struct Frac

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pub struct Frac<T, const TOTAL: u64 = 2> { /* private fields */ }
Expand description

Token that maintains fractional access to some resource. This allows multiple clients to obtain shared references to some resource via borrow.

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impl<T, const TOTAL: u64> Frac<T, TOTAL>

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pub closed spec fn id(self) -> Loc

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pub closed spec fn resource(self) -> T

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pub closed spec fn frac(self) -> int

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pub open spec fn valid(self, id: Loc, frac: int) -> bool

{
    &&& self.id() == id
    &&& self.frac() == frac

}
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pub proof fn new(tracked v: T) -> tracked result : Self

requires
TOTAL > 0,
ensures
result.frac() == TOTAL as int,
result.resource() == v,

Create a fractional token that maintains shared access to the input resource.

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pub proof fn agree(tracked &self, tracked other: &Self)

requires
self.id() == other.id(),
ensures
self.resource() == other.resource(),

Two tokens agree on values of the underlying resource.

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pub proof fn split(tracked &mut self, n: int) -> tracked result : Self

requires
0 < n < old(self).frac(),
ensures
result.id() == self.id() == old(self).id(),
self.resource() == old(self).resource(),
result.resource() == old(self).resource(),
self.frac() + result.frac() == old(self).frac(),
result.frac() == n,

Split one token into two tokens whose quantities sum to the original. The returned token has quantity n; the new value of the input token has quantity old(self).frac() - n.

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pub proof fn combine(tracked &mut self, tracked other: Self)

requires
old(self).id() == other.id(),
ensures
self.id() == old(self).id(),
self.resource() == old(self).resource(),
self.resource() == other.resource(),
self.frac() == old(self).frac() + other.frac(),

Combine two tokens, summing their quantities.

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pub proof fn bounded(tracked &self)

ensures
0 < self.frac() <= TOTAL,

Allowed values for a token’s quantity.

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pub proof fn borrow(tracked &self) -> tracked ret : &T

ensures
ret == self.resource(),

Obtain shared access to the underlying resource.

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pub proof fn take_resource(tracked self) -> tracked pair : (T, Empty<T, TOTAL>)

requires
self.frac() == TOTAL,
ensures
pair.0 == self.resource(),
pair.1.id() == self.id(),

Reclaim full ownership of the underlying resource.

Auto Trait Implementations§

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impl<T, const TOTAL: u64> Freeze for Frac<T, TOTAL>

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impl<T, const TOTAL: u64> RefUnwindSafe for Frac<T, TOTAL>
where T: RefUnwindSafe,

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impl<T, const TOTAL: u64> Send for Frac<T, TOTAL>
where T: Send + Sync,

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impl<T, const TOTAL: u64> Sync for Frac<T, TOTAL>
where T: Sync + Send,

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impl<T, const TOTAL: u64> Unpin for Frac<T, TOTAL>
where T: Unpin,

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impl<T, const TOTAL: u64> UnwindSafe for Frac<T, TOTAL>
where T: UnwindSafe,

Blanket Implementations§

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.