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Prefer Option::map/etc over match wherever it improves clarity #52658

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Jul 25, 2018
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11 changes: 4 additions & 7 deletions src/libcore/str/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -696,13 +696,10 @@ impl<'a> Iterator for CharIndices<'a> {
impl<'a> DoubleEndedIterator for CharIndices<'a> {
#[inline]
fn next_back(&mut self) -> Option<(usize, char)> {
match self.iter.next_back() {
None => None,
Some(ch) => {
let index = self.front_offset + self.iter.iter.len();
Some((index, ch))
}
}
self.iter.next_back().map(|ch| {
let index = self.front_offset + self.iter.iter.len();
(index, ch)
})
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The other possibility for code like this is to let ch = self.iter.next_back()?;, though I don't know if that's better, nor if it's canonical style.

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Ooh, I forgot ? had been extended to support more than just Result types. If you want, I can spin up another PR for that - as it looks like these commits were just merged - but otherwise I suppose I'll just leave this be.

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I'm not confident that it's better, so it's probably not worth bothering with changing -- going to something other than the manual match, as you did, is the important part here.

}
}

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9 changes: 4 additions & 5 deletions src/librustc/traits/on_unimplemented.rs
Original file line number Diff line number Diff line change
Expand Up @@ -190,11 +190,10 @@ impl<'a, 'gcx, 'tcx> OnUnimplementedDirective {
for command in self.subcommands.iter().chain(Some(self)).rev() {
if let Some(ref condition) = command.condition {
if !attr::eval_condition(condition, &tcx.sess.parse_sess, &mut |c| {
options.contains(&(c.name().as_str().to_string(),
match c.value_str().map(|s| s.as_str().to_string()) {
Some(s) => Some(s),
None => None
}))
options.contains(&(
c.name().as_str().to_string(),
c.value_str().map(|s| s.as_str().to_string())
))
}) {
debug!("evaluate: skipping {:?} due to condition", command);
continue
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13 changes: 5 additions & 8 deletions src/librustc/ty/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -2697,15 +2697,12 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
self.opt_associated_item(def_id)
};

match item {
Some(trait_item) => {
match trait_item.container {
TraitContainer(_) => None,
ImplContainer(def_id) => Some(def_id),
}
item.and_then(|trait_item|
match trait_item.container {
TraitContainer(_) => None,
ImplContainer(def_id) => Some(def_id),
}
None => None
}
)
}

/// Looks up the span of `impl_did` if the impl is local; otherwise returns `Err`
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17 changes: 7 additions & 10 deletions src/librustc_metadata/locator.rs
Original file line number Diff line number Diff line change
Expand Up @@ -824,17 +824,14 @@ impl<'a> Context<'a> {
if rlib.is_none() && rmeta.is_none() && dylib.is_none() {
return None;
}
match slot {
Some((_, metadata)) => {
Some(Library {
dylib,
rlib,
rmeta,
metadata,
})
slot.map(|(_, metadata)|
Library {
dylib,
rlib,
rmeta,
metadata,
}
None => None,
}
)
}
}

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5 changes: 1 addition & 4 deletions src/libstd/net/parser.rs
Original file line number Diff line number Diff line change
Expand Up @@ -53,10 +53,7 @@ impl<'a> Parser<'a> {
F: FnOnce(&mut Parser) -> Option<T>,
{
self.read_atomically(move |p| {
match cb(p) {
Some(x) => if p.is_eof() {Some(x)} else {None},
None => None,
}
cb(p).filter(|_| p.is_eof())
})
}

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5 changes: 1 addition & 4 deletions src/libstd/path.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1065,10 +1065,7 @@ impl<'a> Iterator for Ancestors<'a> {

fn next(&mut self) -> Option<Self::Item> {
let next = self.next;
self.next = match next {
Some(path) => path.parent(),
None => None,
};
self.next = next.and_then(Path::parent);
next
}
}
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9 changes: 4 additions & 5 deletions src/libstd/sys_common/backtrace.rs
Original file line number Diff line number Diff line change
Expand Up @@ -156,16 +156,15 @@ pub fn log_enabled() -> Option<PrintFormat> {
_ => return Some(PrintFormat::Full),
}

let val = match env::var_os("RUST_BACKTRACE") {
Some(x) => if &x == "0" {
let val = env::var_os("RUST_BACKTRACE").and_then(|x|
if &x == "0" {
None
} else if &x == "full" {
Some(PrintFormat::Full)
} else {
Some(PrintFormat::Short)
},
None => None,
};
}
);
ENABLED.store(match val {
Some(v) => v as isize,
None => 1,
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12 changes: 4 additions & 8 deletions src/libsyntax_ext/deriving/generic/ty.rs
Original file line number Diff line number Diff line change
Expand Up @@ -138,17 +138,13 @@ pub fn nil_ty<'r>() -> Ty<'r> {
}

fn mk_lifetime(cx: &ExtCtxt, span: Span, lt: &Option<&str>) -> Option<ast::Lifetime> {
match *lt {
Some(s) => Some(cx.lifetime(span, Ident::from_str(s))),
None => None,
}
lt.map(|s|
cx.lifetime(span, Ident::from_str(s))
)
}

fn mk_lifetimes(cx: &ExtCtxt, span: Span, lt: &Option<&str>) -> Vec<ast::Lifetime> {
match *lt {
Some(s) => vec![cx.lifetime(span, Ident::from_str(s))],
None => vec![],
}
mk_lifetime(cx, span, lt).into_iter().collect()
}

impl<'a> Ty<'a> {
Expand Down