## FnParseMode

# Struct FnParseMode

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    pub(crate) struct FnParseMode {
        pub(super) req_name: fn(Edition, IsDotDotDot) -> bool,
        pub(super) context: FnContext,
        pub(super) req_body: bool,
    }

Expand description

Parsing configuration for functions.

The syntax of function items is slightly different within trait definitions, impl blocks, and modules. It is still parsed using the same code, just with different flags set, so that even when the input is wrong and produces a parse error, it still gets into the AST and the rest of the parser and type checker can run.

## Fields§

§`req_name: fn(Edition, IsDotDotDot) -> bool`

A function pointer that decides if, per-parameter `p`, `p` must have a pattern or just a type. This field affects parsing of the parameters list.

    fn foo(alef: A) -> X { X::new() }
           -----^^ affects parsing this part of the function signature
           |
           if req_name returns false, then this name is optional

    fn bar(A) -> X;
           ^
           |
           if req_name returns true, this is an error

Calling this function pointer should only return false if:

- The item is being parsed inside of a trait definition. Within an impl block or a module, it should always evaluate to true.
- The span is from Edition 2015. In particular, you can get a 2015 span inside a 2021 crate using macros.

Or if `IsDotDotDot::Yes`, this function will also return `false` if the item being parsed is inside an `extern` block.

§`context: FnContext`

The context in which this function is parsed, used for diagnostics. This indicates the fn is a free function or method and so on.

§`req_body: bool`

If this flag is set to `true`, then plain, semicolon-terminated function prototypes are not allowed here.

    fn foo(alef: A) -> X { X::new() }
                         ^^^^^^^^^^^^
                         |
                         this is always allowed

    fn bar(alef: A, bet: B) -> X;
                                ^
                                |
                                if req_body is set to true, this is an error

This field should only be set to false if the item is inside of a trait definition or extern block. Within an impl block or a module, it should always be set to true.

## Trait Implementations§

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### impl Clone for FnParseMode

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#### fn clone(&self) -> FnParseMode

Returns a duplicate of the value. Read more
1.0.0 · Source§

#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more
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### impl Copy for FnParseMode

## Auto Trait Implementations§

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### impl DynSend for FnParseMode

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### impl DynSync for FnParseMode

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### impl Freeze for FnParseMode

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### impl RefUnwindSafe for FnParseMode

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### impl Send for FnParseMode

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### impl Sync for FnParseMode

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### impl Unpin for FnParseMode

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### impl UnwindSafe for FnParseMode

## Blanket Implementations§

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### impl<T> Aligned for T

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#### const ALIGN: Alignment

Alignment of `Self`.
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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<'tcx, T> ArenaAllocatable<'tcx, IsCopy> for T
where T: Copy,

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#### fn allocate_on(self, arena: &'tcx Arena<'tcx>) -> &'tcx mut T

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#### fn allocate_from_iter( arena: &'tcx Arena<'tcx>, iter: impl IntoIterator<Item = T>, ) -> &'tcx mut [T]

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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> CloneToUninit for T
where T: Clone,

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#### unsafe fn clone_to_uninit(&self, dest: *mut u8)

🔬This is a nightly-only experimental API. (`clone_to_uninit`)
Performs copy-assignment from `self` to `dest`. Read more
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### impl<T> DynClone for T
where T: Clone,

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#### fn __clone_box(&self, _: Private) -> *mut ()

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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> Instrument for T

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#### fn instrument(self, span: Span) -> Instrumented<Self>

Instruments this type with the provided `Span`, returning an `Instrumented` wrapper. Read more
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#### fn in_current_span(self) -> Instrumented<Self>

Instruments this type with the current `Span`, returning an `Instrumented` wrapper. Read more
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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> IntoEither for T

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#### fn into_either(self, into_left: bool) -> Either<Self, Self>

Converts `self` into a `Left` variant of `Either<Self, Self>` if `into_left` is `true`. Converts `self` into a `Right` variant of `Either<Self, Self>` otherwise. Read more
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#### fn into_either_with<F>(self, into_left: F) -> Either<Self, Self>
where F: FnOnce(&Self) -> bool,

Converts `self` into a `Left` variant of `Either<Self, Self>` if `into_left(&self)` returns `true`. Converts `self` into a `Right` variant of `Either<Self, Self>` otherwise. Read more
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### impl<T> Pointable for T

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#### const ALIGN: usize

The alignment of pointer.
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#### type Init = T

The type for initializers.
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#### unsafe fn init(init: <T as Pointable>::Init) -> usize

Initializes a with the given initializer. Read more
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#### unsafe fn deref<'a>(ptr: usize) -> &'a T

Dereferences the given pointer. Read more
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#### unsafe fn deref_mut<'a>(ptr: usize) -> &'a mut T

Mutably dereferences the given pointer. Read more
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#### unsafe fn drop(ptr: usize)

Drops the object pointed to by the given pointer. Read more
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### impl<T> Same for T

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#### type Output = T

Should always be `Self`
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### impl<T> ToOwned for T
where T: Clone,

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#### type Owned = T

The resulting type after obtaining ownership.
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#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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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.
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### impl<V, T> VZip<V> for T
where V: MultiLane<T>,

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#### fn vzip(self) -> V

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### impl<T> WithSubscriber for T

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#### fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>
where S: Into<Dispatch>,

Attaches the provided `Subscriber` to this type, returning a `WithDispatch` wrapper. Read more
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#### fn with_current_subscriber(self) -> WithDispatch<Self>

Attaches the current default `Subscriber` to this type, returning a `WithDispatch` wrapper. Read more
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### impl<T> ErasedDestructor for T
where T: 'static,

## Layout§

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain `repr(...)` attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 16 bytes