[−][src]Struct frunk::hlist::HNil
Represents the right-most end of a heterogeneous list
Examples
let h = h_cons(1, HNil); let h = h.head; assert_eq!(h, 1);Run
Methods
impl HNil
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pub fn len(&self) -> usize where
HNil: HList,
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HNil: HList,
pub fn prepend<H>(self, h: H) -> HCons<H, HNil> where
HNil: HList,
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HNil: HList,
Prepend an item to the current HList
Examples
let h1 = hlist![1, "hi"]; let h2 = h1.prepend(true); let (a, (b, c)) = h2.into_tuple2(); assert_eq!(a, true); assert_eq!(b, 1); assert_eq!(c, "hi");Run
pub fn sculpt<Ts, Indices>(
self
) -> (Ts, <HNil as Sculptor<Ts, Indices>>::Remainder) where
HNil: Sculptor<Ts, Indices>,
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self
) -> (Ts, <HNil as Sculptor<Ts, Indices>>::Remainder) where
HNil: Sculptor<Ts, Indices>,
Consume the current HList and return an HList with the requested shape.
sculpt
allows us to extract/reshape/scult the current HList into another shape,
provided that the requested shape's types are are contained within the current HList.
The Indices
type parameter allows the compiler to figure out that Ts
and Self
can be morphed into each other.
Examples
let h = hlist![9000, "joe", 41f32, true]; let (reshaped, remainder): (Hlist![f32, i32, &str], _) = h.sculpt(); assert_eq!(reshaped, hlist![41f32, 9000, "joe"]); assert_eq!(remainder, hlist![true]);Run
pub fn into_reverse(self) -> <HNil as IntoReverse>::Output where
HNil: IntoReverse,
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HNil: IntoReverse,
Reverse the HList.
Examples
assert_eq!(hlist![].into_reverse(), hlist![]); assert_eq!( hlist![1, "hello", true, 42f32].into_reverse(), hlist![42f32, true, "hello", 1], )Run
pub fn to_ref<'a>(&'a self) -> <HNil as ToRef<'a>>::Output where
HNil: ToRef<'a>,
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HNil: ToRef<'a>,
Return an HList where the contents are references to the original HList on which this method was called.
Examples
assert_eq!(hlist![].to_ref(), hlist![]); assert_eq!(hlist![1, true].to_ref(), hlist![&1, &true]);Run
pub fn to_mut<'a>(&'a mut self) -> <HNil as ToMut<'a>>::Output where
HNil: ToMut<'a>,
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HNil: ToMut<'a>,
Return an HList
where the contents are mutable references
to the original HList
on which this method was called.
Examples
assert_eq!(hlist![].to_mut(), hlist![]); assert_eq!(hlist![1, true].to_mut(), hlist![&mut 1, &mut true]);Run
pub fn map<F>(self, mapper: F) -> <HNil as HMappable<F>>::Output where
HNil: HMappable<F>,
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HNil: HMappable<F>,
Apply a function to each element of an HList.
This transforms some Hlist![A, B, C, ..., E]
into some
Hlist![T, U, V, ..., Z]
. A variety of types are supported
for the folder argument:
- An
hlist![]
of closures (one for each element). - A single closure (for mapping an HList that is homogenous).
- A single
Poly
.
Examples
use ::frunk::HNil; assert_eq!(HNil.map(HNil), HNil); let h = hlist![1, false, 42f32]; // Sadly we need to help the compiler understand the bool type in our mapper let mapped = h.to_ref().map(hlist![ |&n| n + 1, |b: &bool| !b, |&f| f + 1f32]); assert_eq!(mapped, hlist![2, true, 43f32]); // There is also a value-consuming version that passes values to your functions // instead of just references: let mapped2 = h.map(hlist![ |n| n + 3, |b: bool| !b, |f| f + 8959f32]); assert_eq!(mapped2, hlist![4, true, 9001f32]);Run
pub fn foldl<Folder, Acc>(
self,
folder: Folder,
acc: Acc
) -> <HNil as HFoldLeftable<Folder, Acc>>::Output where
HNil: HFoldLeftable<Folder, Acc>,
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self,
folder: Folder,
acc: Acc
) -> <HNil as HFoldLeftable<Folder, Acc>>::Output where
HNil: HFoldLeftable<Folder, Acc>,
Perform a left fold over an HList.
This transforms some Hlist![A, B, C, ..., E]
into a single
value by visiting all of the elements in left-to-right order.
A variety of types are supported for the mapper argument:
- An
hlist![]
of closures (one for each element). - A single closure (for folding an HList that is homogenous).
The accumulator can freely change type over the course of the call.
When called with a list of N
functions, an expanded form of the
implementation with type annotations might look something like this:
let acc: Acc0 = init_value; let acc: Acc1 = f1(acc, x1); let acc: Acc2 = f2(acc, x2); let acc: Acc3 = f3(acc, x3); ... let acc: AccN = fN(acc, xN); accRun
Examples
let nil = hlist![]; assert_eq!(nil.foldl(hlist![], 0), 0); let h = hlist![1, false, 42f32]; let folded = h.to_ref().foldl( hlist![ |acc, &i| i + acc, |acc, b: &bool| if !b && acc > 42 { 9000f32 } else { 0f32 }, |acc, &f| f + acc ], 1 ); assert_eq!(42f32, folded); // There is also a value-consuming version that passes values to your folding // functions instead of just references: let folded2 = h.foldl( hlist![ |acc, i| i + acc, |acc, b: bool| if !b && acc > 42 { 9000f32 } else { 0f32 }, |acc, f| f + acc ], 8918 ); assert_eq!(9042f32, folded2)Run
pub fn foldr<Folder, Init>(
self,
folder: Folder,
init: Init
) -> <HNil as HFoldRightable<Folder, Init>>::Output where
HNil: HFoldRightable<Folder, Init>,
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self,
folder: Folder,
init: Init
) -> <HNil as HFoldRightable<Folder, Init>>::Output where
HNil: HFoldRightable<Folder, Init>,
Perform a right fold over an HList.
This transforms some Hlist![A, B, C, ..., E]
into a single
value by visiting all of the elements in reverse order.
A variety of types are supported for the mapper argument:
- An
hlist![]
of closures (one for each element). - A single closure (for folding an HList that is homogenous), taken by reference.
The accumulator can freely change type over the course of the call.
Comparison to foldl
While the order of element traversal in foldl
may seem more natural,
foldr
does have its use cases, in particular when it is used to build
something that reflects the structure of the original HList (such as
folding an HList of Option
s into an Option
of an HList).
An implementation of such a function using foldl
will tend to
reverse the list, while foldr
will tend to preserve its order.
The reason for this is because foldr
performs what is known as
"structural induction;" it can be understood as follows:
- Write out the HList in terms of
h_cons
andHNil
. - Substitute each
h_cons
with a function, and substituteHNil
withinit
the list: h_cons(x1, h_cons(x2, h_cons(x3, ...h_cons(xN, HNil))...))) becomes: f1( x1, f2( x2, f3( x3, ... fN( xN, init))...)))Run
Examples
let nil = hlist![]; assert_eq!(nil.foldr(hlist![], 0), 0); let h = hlist![1, false, 42f32]; let folded = h.foldr( hlist![ |i, acc| i + acc, |b: bool, acc| if !b && acc > 42f32 { 9000 } else { 0 }, |f, acc| f + acc ], 1f32 ); assert_eq!(9001, folded)Run
Trait Implementations
impl IntoValueLabelled for HNil
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type Output = HNil
fn into_value_labelled(self) -> <HNil as IntoValueLabelled>::Output
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impl PartialEq<HNil> for HNil
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fn eq(&self, other: &HNil) -> bool
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#[must_use]
fn ne(&self, other: &Rhs) -> bool
1.0.0[src]
This method tests for !=
.
impl IntoUnlabelled for HNil
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Implementation for HNil
type Output = HNil
fn into_unlabelled(self) -> <HNil as IntoUnlabelled>::Output
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impl<F, Acc> HFoldLeftable<F, Acc> for HNil
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impl HList for HNil
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const LEN: usize
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fn static_len() -> usize
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fn length(&self) -> u32
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Please use len() or static_len() instead.
fn len(&self) -> usize
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Returns the length of a given HList Read more
fn prepend<H>(self, h: H) -> HCons<H, Self>
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Prepends an item to the current HList Read more
impl Clone for HNil
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fn clone(&self) -> HNil
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fn clone_from(&mut self, source: &Self)
1.0.0[src]
Performs copy-assignment from source
. Read more
impl<RHS> Add<RHS> for HNil where
RHS: HList,
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RHS: HList,
type Output = RHS
The resulting type after applying the +
operator.
fn add(self, rhs: RHS) -> RHS
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impl PartialOrd<HNil> for HNil
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fn partial_cmp(&self, other: &HNil) -> Option<Ordering>
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#[must_use]
fn lt(&self, other: &Rhs) -> bool
1.0.0[src]
This method tests less than (for self
and other
) and is used by the <
operator. Read more
#[must_use]
fn le(&self, other: &Rhs) -> bool
1.0.0[src]
This method tests less than or equal to (for self
and other
) and is used by the <=
operator. Read more
#[must_use]
fn gt(&self, other: &Rhs) -> bool
1.0.0[src]
This method tests greater than (for self
and other
) and is used by the >
operator. Read more
#[must_use]
fn ge(&self, other: &Rhs) -> bool
1.0.0[src]
This method tests greater than or equal to (for self
and other
) and is used by the >=
operator. Read more
impl From<()> for HNil
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impl IntoReverse for HNil
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type Output = HNil
fn into_reverse(self) -> <HNil as IntoReverse>::Output
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impl Debug for HNil
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impl Copy for HNil
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impl Eq for HNil
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impl<'a> ToMut<'a> for HNil
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impl<'a> ToRef<'a> for HNil
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impl Default for HNil
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impl<F, Init> HFoldRightable<F, Init> for HNil
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impl CoproductEmbedder<CNil, HNil> for CNil
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impl<Head, Tail> CoproductEmbedder<Coproduct<Head, Tail>, HNil> for CNil where
CNil: CoproductEmbedder<Tail, HNil>,
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CNil: CoproductEmbedder<Tail, HNil>,
impl<F> HMappable<F> for HNil
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impl<T> Into<Vec<T>> for HNil
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impl<SourceHead, SourceTail> Transmogrifier<HNil, HNil> for HCons<SourceHead, SourceTail>
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Implementation of Transmogrifier
for when the Target
is empty and the Source
is non-empty.
fn transmogrify(self) -> HNil
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impl Transmogrifier<HNil, HNil> for HNil
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Implementation of Transmogrifier
for when the Target
is empty and the Source
is empty.
fn transmogrify(self) -> HNil
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impl<Choices> CoproductSubsetter<CNil, HNil> for Choices
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type Remainder = Choices
fn subset(
self
) -> Result<CNil, <Choices as CoproductSubsetter<CNil, HNil>>::Remainder>
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self
) -> Result<CNil, <Choices as CoproductSubsetter<CNil, HNil>>::Remainder>
impl Hash for HNil
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fn hash<__H>(&self, state: &mut __H) where
__H: Hasher,
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__H: Hasher,
fn hash_slice<H>(data: &[Self], state: &mut H) where
H: Hasher,
1.3.0[src]
H: Hasher,
Feeds a slice of this type into the given [Hasher
]. Read more
impl<Source> Sculptor<HNil, HNil> for Source
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Implementation for when the target is an empty HList (HNil)
Index type is HNil because we don't need an index for finding HNil
impl Ord for HNil
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fn cmp(&self, other: &HNil) -> Ordering
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fn max(self, other: Self) -> Self
1.21.0[src]
Compares and returns the maximum of two values. Read more
fn min(self, other: Self) -> Self
1.21.0[src]
Compares and returns the minimum of two values. Read more
fn clamp(self, min: Self, max: Self) -> Self
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clamp
)Returns max if self is greater than max, and min if self is less than min. Otherwise this will return self. Panics if min > max. Read more
impl Semigroup for HNil
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Since () + () = (), the same is true for HNil
Auto Trait Implementations
Blanket Implementations
impl<T, U> Into for T where
U: From<T>,
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U: From<T>,
impl<T> ToOwned for T where
T: Clone,
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T: Clone,
impl<T> From for T
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impl<T, U> TryFrom for T where
U: Into<T>,
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U: Into<T>,
type Error = Infallible
The type returned in the event of a conversion error.
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
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impl<T> Borrow for T where
T: ?Sized,
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T: ?Sized,
impl<T> Any for T where
T: 'static + ?Sized,
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T: 'static + ?Sized,
impl<T> BorrowMut for T where
T: ?Sized,
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T: ?Sized,
fn borrow_mut(&mut self) -> &mut T
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impl<T, U> TryInto for T where
U: TryFrom<T>,
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U: TryFrom<T>,
type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
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impl<Choices> CoproductSubsetter for Choices
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type Remainder = Choices
fn subset(
self
) -> Result<CNil, <Choices as CoproductSubsetter<CNil, HNil>>::Remainder>
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self
) -> Result<CNil, <Choices as CoproductSubsetter<CNil, HNil>>::Remainder>
impl<Source> Sculptor for Source
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impl<T, U, I> LiftInto for T where
U: LiftFrom<T, I>,
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U: LiftFrom<T, I>,