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Calculate the exact capacity for 2 HashMaps #52435

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Merged
merged 1 commit into from
Jul 17, 2018
Merged

Calculate the exact capacity for 2 HashMaps #52435

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2 changes: 1 addition & 1 deletion src/bootstrap/metadata.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -51,7 +51,7 @@ pub fn build(build: &mut Build) {
build_krate("", build, &mut resolves, "src/libtest");
build_krate(&build.rustc_features(), build, &mut resolves, "src/rustc");

let mut id2name = HashMap::new();
let mut id2name = HashMap::with_capacity(build.crates.len());
for (name, krate) in build.crates.iter() {
id2name.insert(krate.id.clone(), name.clone());
}
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For what it's worth, this one could also be done with map() followed by collect().

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3 changes: 2 additions & 1 deletion src/librustc_driver/profile/trace.rs
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Expand Up @@ -220,7 +220,8 @@ pub fn write_counts(count_file: &mut File, counts: &mut HashMap<String,QueryMetr
}

pub fn write_traces(html_file: &mut File, counts_file: &mut File, traces: &Vec<Rec>) {
let mut counts : HashMap<String,QueryMetric> = HashMap::new();
let capacity = traces.iter().fold(0, |acc, t| acc + 1 + t.extent.len());
let mut counts : HashMap<String, QueryMetric> = HashMap::with_capacity(capacity);
compute_counts_rec(&mut counts, traces);
write_counts(counts_file, &mut counts);

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