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Simplify calling find_implied_output_region. #38036

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Merged
merged 1 commit into from
Dec 6, 2016
Merged

Simplify calling find_implied_output_region. #38036

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32 changes: 15 additions & 17 deletions src/librustc_typeck/astconv.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -538,14 +538,15 @@ impl<'o, 'gcx: 'tcx, 'tcx> AstConv<'gcx, 'tcx>+'o {
/// Returns the appropriate lifetime to use for any output lifetimes
/// (if one exists) and a vector of the (pattern, number of lifetimes)
/// corresponding to each input type/pattern.
fn find_implied_output_region<F>(&self,
fn find_implied_output_region<I>(&self,
input_tys: &[Ty<'tcx>],
input_pats: F) -> ElidedLifetime
where F: FnOnce() -> Vec<String>
input_pats: I) -> ElidedLifetime
where I: Iterator<Item=String>
{
let tcx = self.tcx();
let mut lifetimes_for_params = Vec::new();
let mut lifetimes_for_params = Vec::with_capacity(input_tys.len());
let mut possible_implied_output_region = None;
let mut lifetimes = 0;

for input_type in input_tys.iter() {
let mut regions = FxHashSet();
Expand All @@ -554,7 +555,9 @@ impl<'o, 'gcx: 'tcx, 'tcx> AstConv<'gcx, 'tcx>+'o {
debug!("find_implied_output_regions: collected {:?} from {:?} \
have_bound_regions={:?}", &regions, input_type, have_bound_regions);

if regions.len() == 1 {
lifetimes += regions.len();

if lifetimes == 1 && regions.len() == 1 {
// there's a chance that the unique lifetime of this
// iteration will be the appropriate lifetime for output
// parameters, so lets store it.
Expand All @@ -571,12 +574,12 @@ impl<'o, 'gcx: 'tcx, 'tcx> AstConv<'gcx, 'tcx>+'o {
});
}

if lifetimes_for_params.iter().map(|e| e.lifetime_count).sum::<usize>() == 1 {
if lifetimes == 1 {
Ok(*possible_implied_output_region.unwrap())
} else {
// Fill in the expensive `name` fields now that we know they're
// needed.
for (info, input_pat) in lifetimes_for_params.iter_mut().zip(input_pats()) {
for (info, input_pat) in lifetimes_for_params.iter_mut().zip(input_pats) {
info.name = input_pat;
}
Err(Some(lifetimes_for_params))
Expand Down Expand Up @@ -615,8 +618,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> AstConv<'gcx, 'tcx>+'o {
let inputs = self.tcx().mk_type_list(data.inputs.iter().map(|a_t| {
self.ast_ty_arg_to_ty(&binding_rscope, None, region_substs, a_t)
}));
let inputs_len = inputs.len();
let input_params = || vec![String::new(); inputs_len];
let input_params = iter::repeat(String::new()).take(inputs.len());
let implied_output_region = self.find_implied_output_region(&inputs, input_params);

let (output, output_span) = match data.output {
Expand Down Expand Up @@ -1776,14 +1778,10 @@ impl<'o, 'gcx: 'tcx, 'tcx> AstConv<'gcx, 'tcx>+'o {
let implied_output_region = match explicit_self {
Some(ExplicitSelf::ByReference(region, _)) => Ok(*region),
_ => {
// `pat_to_string` is expensive and
// `find_implied_output_region` only needs its result when
// there's an error. So we wrap it in a closure to avoid
// calling it until necessary.
let arg_pats = || {
arg_params.iter().map(|a| pprust::pat_to_string(&a.pat)).collect()
};
self.find_implied_output_region(&arg_tys, arg_pats)
self.find_implied_output_region(&arg_tys,
arg_params.iter()
.map(|a| pprust::pat_to_string(&a.pat)))

}
};

Expand Down