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Use take_while instead of scan in impl of Product, Sum and FromStream for Option and Result #667

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merged 6 commits into from
Jan 27, 2020
Merged

Use take_while instead of scan in impl of Product, Sum and FromStream for Option and Result #667

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83afbab
Use `take_while` instead of `scan` for `Option`
olegnn Jan 12, 2020
fb567a3
Recovered comments
olegnn Jan 12, 2020
134089a
Use `filter_map(identity)` + other fixes
olegnn Jan 15, 2020
38de0bf
Use `std::convert::identity`
olegnn Jan 15, 2020
ed24801
Use internal `scan` state in `Result`s implementation
olegnn Jan 15, 2020
ed7ddac
Rewrote `Result`s implementation using `take_while` and `filter_map`
olegnn Jan 17, 2020
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25 changes: 14 additions & 11 deletions src/option/from_stream.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@ use std::pin::Pin;

use crate::prelude::*;
use crate::stream::{FromStream, IntoStream};
use crate::utils::identity;

impl<T, V> FromStream<Option<T>> for Option<V>
where
Expand All @@ -17,24 +18,26 @@ where
let stream = stream.into_stream();

Box::pin(async move {
// Using `scan` here because it is able to stop the stream early
// Using `take_while` here because it is able to stop the stream early
// if a failure occurs
let mut found_error = false;
let mut found_none = false;
let out: V = stream
.scan((), |_, elem| {
match elem {
Some(elem) => Some(elem),
None => {
found_error = true;
// Stop processing the stream on error
None
}
.take_while(|elem| {
elem.is_some() || {
found_none = true;
// Stop processing the stream on `None`
false
}
})
.filter_map(identity)
.collect()
.await;

if found_error { None } else { Some(out) }
if found_none {
None
} else {
Some(out)
}
})
}
}
27 changes: 15 additions & 12 deletions src/option/product.rs
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Original file line number Diff line number Diff line change
@@ -1,7 +1,8 @@
use std::pin::Pin;

use crate::prelude::*;
use crate::stream::{Stream, Product};
use crate::stream::{Product, Stream};
use crate::utils::identity;

impl<T, U> Product<Option<U>> for Option<T>
where
Expand Down Expand Up @@ -36,23 +37,25 @@ where
```
"#]
fn product<'a, S>(stream: S) -> Pin<Box<dyn Future<Output = Option<T>> + 'a>>
where S: Stream<Item = Option<U>> + 'a
where
S: Stream<Item = Option<U>> + 'a,
{
Box::pin(async move {
// Using `scan` here because it is able to stop the stream early
// Using `take_while` here because it is able to stop the stream early
// if a failure occurs
let mut found_none = false;
let out = <T as Product<U>>::product(stream
.scan((), |_, elem| {
match elem {
Some(elem) => Some(elem),
None => {
let out = <T as Product<U>>::product(
stream
.take_while(|elem| {
elem.is_some() || {
found_none = true;
// Stop processing the stream on error
None
// Stop processing the stream on `None`
false
}
}
})).await;
})
.filter_map(identity),
)
.await;

if found_none {
None
Expand Down
25 changes: 14 additions & 11 deletions src/option/sum.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@ use std::pin::Pin;

use crate::prelude::*;
use crate::stream::{Stream, Sum};
use crate::utils::identity;

impl<T, U> Sum<Option<U>> for Option<T>
where
Expand Down Expand Up @@ -31,23 +32,25 @@ where
```
"#]
fn sum<'a, S>(stream: S) -> Pin<Box<dyn Future<Output = Option<T>> + 'a>>
where S: Stream<Item = Option<U>> + 'a
where
S: Stream<Item = Option<U>> + 'a,
{
Box::pin(async move {
// Using `scan` here because it is able to stop the stream early
// Using `take_while` here because it is able to stop the stream early
// if a failure occurs
let mut found_none = false;
let out = <T as Sum<U>>::sum(stream
.scan((), |_, elem| {
match elem {
Some(elem) => Some(elem),
None => {
let out = <T as Sum<U>>::sum(
stream
.take_while(|elem| {
elem.is_some() || {
found_none = true;
// Stop processing the stream on error
None
// Stop processing the stream on `None`
false
}
}
})).await;
})
.filter_map(identity),
)
.await;

if found_none {
None
Expand Down
2 changes: 1 addition & 1 deletion src/result/from_stream.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -21,7 +21,7 @@ where
// if a failure occurs
let mut found_error = None;
let out: V = stream
.scan((), |_, elem| {
.scan((), |(), elem| {
match elem {
Ok(elem) => Some(elem),
Err(err) => {
Expand Down
28 changes: 15 additions & 13 deletions src/result/product.rs
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
use std::pin::Pin;

use crate::prelude::*;
use crate::stream::{Stream, Product};
use crate::stream::{Product, Stream};

impl<T, U, E> Product<Result<U, E>> for Result<T, E>
where
Expand Down Expand Up @@ -36,26 +36,28 @@ where
```
"#]
fn product<'a, S>(stream: S) -> Pin<Box<dyn Future<Output = Result<T, E>> + 'a>>
where S: Stream<Item = Result<U, E>> + 'a
where
S: Stream<Item = Result<U, E>> + 'a,
{
Box::pin(async move {
// Using `scan` here because it is able to stop the stream early
// if a failure occurs
let mut found_error = None;
let out = <T as Product<U>>::product(stream
.scan((), |_, elem| {
match elem {
Ok(elem) => Some(elem),
Err(err) => {
found_error = Some(err);
// Stop processing the stream on error
None
}
let out = <T as Product<U>>::product(stream.scan((), |(), elem| {
match elem {
Ok(elem) => Some(elem),
Err(err) => {
found_error = Some(err);
// Stop processing the stream on error
None
}
})).await;
}
}))
.await;

match found_error {
Some(err) => Err(err),
None => Ok(out)
None => Ok(out),
}
})
}
Expand Down
26 changes: 14 additions & 12 deletions src/result/sum.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -36,26 +36,28 @@ where
```
"#]
fn sum<'a, S>(stream: S) -> Pin<Box<dyn Future<Output = Result<T, E>> + 'a>>
where S: Stream<Item = Result<U, E>> + 'a
where
S: Stream<Item = Result<U, E>> + 'a,
{
Box::pin(async move {
// Using `scan` here because it is able to stop the stream early
// if a failure occurs
let mut found_error = None;
let out = <T as Sum<U>>::sum(stream
.scan((), |_, elem| {
match elem {
Ok(elem) => Some(elem),
Err(err) => {
found_error = Some(err);
// Stop processing the stream on error
None
}
let out = <T as Sum<U>>::sum(stream.scan((), |(), elem| {
match elem {
Ok(elem) => Some(elem),
Err(err) => {
found_error = Some(err);
// Stop processing the stream on error
None
}
})).await;
}
}))
.await;

match found_error {
Some(err) => Err(err),
None => Ok(out)
None => Ok(out),
}
})
}
Expand Down
2 changes: 1 addition & 1 deletion src/unit/from_stream.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,6 @@ impl FromStream<()> for () {
fn from_stream<'a, S: IntoStream<Item = ()> + 'a>(
stream: S,
) -> Pin<Box<dyn Future<Output = Self> + 'a>> {
Box::pin(stream.into_stream().for_each(|_| ()))
Box::pin(stream.into_stream().for_each(drop))
}
}
8 changes: 8 additions & 0 deletions src/utils.rs
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Expand Up @@ -52,6 +52,14 @@ pub fn random(n: u32) -> u32 {
})
}

/// Returns given argument without changes.
#[allow(dead_code)]
#[doc(hidden)]
#[inline(always)]
pub(crate) fn identity<T>(arg: T) -> T {
arg
}

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/// Add additional context to errors
pub(crate) trait Context {
fn context(self, message: impl Fn() -> String) -> Self;
Expand Down