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</pre></div><pre class="rust"><code><span class="kw">use </span>std::ptr::NonNull;
<span class="doccomment">/// Indicates that a field is unsafe to write to, since we have to uphold certain invariants.
/// Make sure to document them!
///
/// # Safety
/// - **Declaring** this struct is unsafe.
/// - within a struct, all fields should have a different associated constant, I would suggest just
/// numbering them from 0.
///
/// ```rs
/// type Boolean = u8;
/// let mut valid_bool = unsafe { UnsafeField::new(true as Boolean) };
/// let mut always_3 = unsafe { UnsafeField::new(3) };
/// // UB
/// mem::swap(valid_bool, always_3);
/// ```
///
/// # Theoretical Best Implementation
///
/// A better implementation of this is not possible without a macro. I would consider a macro
/// implementation a good enough proof for item-only scoping being possible all the time. This is
/// perhaps a bad name, but item-only scoping, means that we can write (all?) unsafe code to be
/// verifiably sound at item-scope, this includes
///
/// - Struct declaration
/// - Struct construction
/// - Function declaration
/// - Function calling
///
/// For example, in the case of `LongString`, the following declaration is unsound. This is is
/// because the type `usize` does not follow the same contract as the field `len`, therefore it is
/// and unsafe type to use for `len`. As a result, we must mark it as such. The same is the case
/// for all other fields, since they all have invariants.
///
/// ```rs
/// /// # Safety
/// /// - `len` must be constrained by [len invariants] at all times
/// /// - `capacity` must be contrained by [capacity invariants] at all times
/// /// - `buf` must constrained by [buf invaraiants] at all times
/// struct LongString {
/// len: usize,
/// capacity: usize,
/// buf: RawBuf<usize>,
/// }
/// ```
///
/// Our declaration should soundly look like this:
///
/// ```rs
/// struct LongString {
/// unsafe len: usize,
/// unsafe capacity: usize,
/// unsafe buf: RawBuf<usize>,
/// }
/// ```
///
/// More formally, the encapsulation of struct-declaration unsafe scoping is as follows:
/// - A safety contract must be written above the struct declaration
/// - The safety contract must include **only** the invariants for each type. These invariants
/// should ideally be upheld *at all times*. I would suggest *always*, but this might not allow
/// for all possible data structures... I have a hunch it is though.
/// - If a field has an invariant that is already encapsulated safely by the type it is assigned,
/// we do not need to write about that invariant (though you can if you want??)
/// - If a field has an invariant that is not encapsulated safely by the type it is assigned, you
/// MUST declare it as `unsafe`.
///
/// It is potentially not obvious why this is encapsulated at the item level. Consider
/// function-execution unsafe scoping. The function defines a contract, and if we fulfill that
/// contract, we can execute the function *completely safely*. Generally,
///
/// 1. Define a contract for an unsafe item, such that
/// 2. if we validate that contract
/// 3. we can use the item safely
///
/// With struct-declaration unsafe scoping, we are doing essentially the same thing:
///
/// 1. Define a contract (for an unsafe item?) such that
/// 2. if we validate that contract (define the struct properly)
/// 3. we can use the item safely (define methods on the struct etc.)
///
/// The bit "for an unsafe item" might cause some disagreement. Who's to say that something is an
/// unsafe item? Well, in this world all struct declarations are unsafe, except for those without
/// a safety contract... Actually, that's the same as all functions in this world. All functions
/// are unsafe, except for those without a safety contract.
</span><span class="attr">#[derive(Clone, Copy)]
</span><span class="kw">pub struct </span>UnsafeField<T, <span class="kw">const </span>FIELD_INDEX: usize>(T);
<span class="kw">impl</span><T, <span class="kw">const </span>FIELD_INDEX: usize> UnsafeField<T, FIELD_INDEX> {
<span class="doccomment">/// Return a reference to the underlying value
</span><span class="kw">pub const fn </span>get(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="kw-2">&</span>T {
<span class="kw-2">&</span><span class="self">self</span>.<span class="number">0
</span>}
<span class="kw">pub fn </span>own(<span class="self">self</span>) -> T {
<span class="self">self</span>.<span class="number">0
</span>}
}
<span class="kw">impl</span><T, <span class="kw">const </span>FIELD_INDEX: usize> UnsafeAssign<T> <span class="kw">for </span>UnsafeField<T, FIELD_INDEX> {
<span class="kw">unsafe fn </span>new(value: T) -> <span class="self">Self </span>{
<span class="self">Self</span>(value)
}
<span class="kw">unsafe fn </span>set(<span class="kw-2">&mut </span><span class="self">self</span>, value: T) {
<span class="self">self</span>.<span class="number">0 </span>= value;
}
<span class="kw">fn </span>get_mut(<span class="kw-2">&mut </span><span class="self">self</span>) -> NonNull<T> {
NonNull::from(<span class="kw-2">&mut </span><span class="self">self</span>.<span class="number">0</span>)
}
}
<span class="kw">pub trait </span>UnsafeAssign<T>
<span class="kw">where
</span><span class="self">Self</span>: Sized,
{
<span class="doccomment">/// Constructs a new [`UnsafeField`]
///
/// # Safety
/// - must uphold all invariants of the field
</span><span class="kw">unsafe fn </span>new(value: T) -> <span class="self">Self</span>;
<span class="doccomment">/// Sets the underyling value to `value`
///
/// # Safety
/// - must uphold all invariants of the field
</span><span class="kw">unsafe fn </span>set(<span class="kw-2">&mut </span><span class="self">self</span>, value: T);
<span class="doccomment">/// Gets a raw pointer to the value
///
/// # Safety
/// - msut uphold all invaraints when assigning the pointer
</span><span class="kw">fn </span>get_mut(<span class="kw-2">&mut </span><span class="self">self</span>) -> NonNull<T>;
}
<span class="doccomment">/// Assign several [`UnsafeField`] 'simultaneously'.
///
/// There might be occasions where we cannot assign multiple fields simultaenously by
/// reconstructing the struct (though this should be done in most cases). In this case, we
/// can enforce a slightly lesser form of safety, by upholding invariants "only when the struct"
/// is read from. This pattern guarantees that we cannot get a `&self` in between writes to
/// fields.
///
/// ```rs
/// unsafe_field::SimultaneousUnsafeAssignment
/// .with(&mut foo.field_1, 5)
/// .with(&mut foo.field_2, 10)
/// .with(&mut foo.field_3, 15)
/// .set_all();
/// ```
///
/// # Safety
///
/// - ensure that all invariants are upheld after all assignments are complete
/// - you must not rely on the ordering of the assignments, that is, the Unit state should
/// be the same no matter the order of the assignments. This should be trivially verifiable,
/// since I'm pretty sure it's impossible. Just putting it in here in case someon can find
/// a way of doing this.
///
/// # Implementation Notes
///
/// This is possible to implement without storing references to the fields, but I don't think it
/// should matter in the Unit. This is probably optimised to the same thing? Not sure though.
/// I don't think it matters that much.
///
/// There's probably some kind of way of doing this with pure functions that inlines functions
/// more aggressively, as well.
</span><span class="kw">pub struct </span>SimultaneousUnsafeAssignment;
<span class="kw">impl </span>SimultaneousUnsafeAssignment {
<span class="kw">pub fn </span>with<<span class="lifetime">'b</span>, Dst: UnsafeAssign<T>, T>(
<span class="self">self</span>,
value: T,
dst: <span class="kw-2">&</span><span class="lifetime">'b </span><span class="kw-2">mut </span>Dst,
) -> DeferredSimultaneousUnsafeAssignment<<span class="self">Self</span>, DeferredUnsafeAssignment<<span class="lifetime">'b</span>, Dst, T>> {
DeferredSimultaneousUnsafeAssignment {
first: <span class="self">self</span>,
second: DeferredUnsafeAssignment { field: dst, value },
}
}
}
<span class="kw">impl </span>SimultaneousUnsafeAssign <span class="kw">for </span>SimultaneousUnsafeAssignment {
<span class="kw">unsafe fn </span>set_all(<span class="self">self</span>) {}
}
<span class="kw">pub trait </span>SimultaneousUnsafeAssign {
<span class="doccomment">/// Complete all assignments that have been deferred 'simultaneously'. This is not actually
/// simultaneous, but ensures that all values are assigned, without the struct they are a
/// part of being read in an invalid state
///
/// # Safety
/// - ensure that all invariants are upheld after all assignments are complete
</span><span class="kw">unsafe fn </span>set_all(<span class="self">self</span>);
}
<span class="kw">pub struct </span>DeferredSimultaneousUnsafeAssignment<
First: SimultaneousUnsafeAssign,
Second: SimultaneousUnsafeAssign,
> {
first: First,
second: Second,
}
<span class="kw">impl</span><First: SimultaneousUnsafeAssign, Second: SimultaneousUnsafeAssign>
DeferredSimultaneousUnsafeAssignment<First, Second>
{
<span class="kw">pub fn </span>with<<span class="lifetime">'b</span>, Dst: UnsafeAssign<T>, T>(
<span class="self">self</span>,
value: T,
dst: <span class="kw-2">&</span><span class="lifetime">'b </span><span class="kw-2">mut </span>Dst,
) -> DeferredSimultaneousUnsafeAssignment<<span class="self">Self</span>, DeferredUnsafeAssignment<<span class="lifetime">'b</span>, Dst, T>> {
DeferredSimultaneousUnsafeAssignment {
first: <span class="self">self</span>,
second: DeferredUnsafeAssignment { field: dst, value },
}
}
}
<span class="kw">impl</span><<span class="lifetime">'a</span>, First: SimultaneousUnsafeAssign, Second: SimultaneousUnsafeAssign> SimultaneousUnsafeAssign
<span class="kw">for </span>DeferredSimultaneousUnsafeAssignment<First, Second>
{
<span class="kw">unsafe fn </span>set_all(<span class="self">self</span>) {
<span class="self">self</span>.first.set_all();
<span class="self">self</span>.second.set_all();
}
}
<span class="kw">pub struct </span>DeferredUnsafeAssignment<<span class="lifetime">'a</span>, Dst: UnsafeAssign<T>, T> {
field: <span class="kw-2">&</span><span class="lifetime">'a </span><span class="kw-2">mut </span>Dst,
value: T,
}
<span class="kw">impl</span><<span class="lifetime">'a</span>, Dst: UnsafeAssign<T>, T> DeferredUnsafeAssignment<<span class="lifetime">'a</span>, Dst, T> {
<span class="kw">pub fn </span>with<<span class="lifetime">'b</span>, UDst: UnsafeAssign<U>, U>(
<span class="self">self</span>,
value: U,
dst: <span class="kw-2">&</span><span class="lifetime">'b </span><span class="kw-2">mut </span>UDst,
) -> DeferredSimultaneousUnsafeAssignment<<span class="self">Self</span>, DeferredUnsafeAssignment<<span class="lifetime">'b</span>, UDst, U>> {
DeferredSimultaneousUnsafeAssignment {
first: <span class="self">self</span>,
second: DeferredUnsafeAssignment { field: dst, value },
}
}
}
<span class="kw">impl</span><<span class="lifetime">'a</span>, Dst: UnsafeAssign<T>, T> SimultaneousUnsafeAssign
<span class="kw">for </span>DeferredUnsafeAssignment<<span class="lifetime">'a</span>, Dst, T>
{
<span class="kw">unsafe fn </span>set_all(<span class="self">self</span>) {
<span class="self">self</span>.field.set(<span class="self">self</span>.value);
}
}
</code></pre></div></section></main></body></html>