use structopt instead of clap directly

BENCHMARKING.md

@@ -71,3 +71,17 @@ Benchmark #1: ./target/release/similar-sort benchmark < /usr/share/dict/words
 ```
 
 So, no to that too!
+
+## Removing arg parsing overhead?
+
+What if it's creating that big Clap struct that's causing problems?
+Let's give structopt a try (and then move to deriving from Clap once 3.0.0 is finally released.)
+
+```
+$ hyperfine './target/release/similar-sort benchmark < /usr/share/dict/words'
+Benchmark #1: ./target/release/similar-sort benchmark < /usr/share/dict/words
+  Time (mean ± σ):     667.5 ms ±   7.1 ms    [User: 4.158 s, System: 0.031 s]
+  Range (min … max):   658.3 ms … 678.2 ms    10 runs
+```
+
+Ok, seems fine!

Cargo.toml

@@ -7,7 +7,7 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-clap = "2.33.3"
+structopt = "0.3.22"
 color-eyre = "0.5.7"
 rayon = "1.5.1"
 strsim = "0.10.0"

src/main.rs

@@ -1,8 +1,17 @@
-use clap::{crate_authors, crate_version, App, Arg};
-use color_eyre::eyre::{ContextCompat, Result, WrapErr};
+use color_eyre::eyre::{Result, WrapErr};
 use rayon::prelude::*;
 use std::io::{self, stdin, stdout, BufRead, BufWriter, Write};
 use strsim::levenshtein;
+use structopt::StructOpt;
+
+// works like `sort`, but sorts according to Levenshtein distance instead of
+// alphanumerically.
+#[derive(StructOpt)]
+#[structopt(name = "similar-sort")]
+struct Opts {
+    /// sort according to distance from this string
+    target: String,
+}
 
 fn main() {
     if let Err(err) = try_main() {
@@ -14,28 +23,15 @@ fn main() {
 fn try_main() -> Result<()> {
     color_eyre::install()?;
 
-    let matches = App::new("similar-sort")
-        .version(crate_version!())
-        .author(crate_authors!())
-        .about("works like `sort`, but sorts according to Levenshtein distance instead of alphanumerically")
-        .arg(
-            Arg::with_name("target")
-                .value_name("TARGET")
-                .help("sort according to distance from this string")
-                .required(true)
-        ).get_matches();
-
-    let target = matches.value_of("target").context(
-        "could not get the target value. This is an internal error and should be reported.",
-    )?;
+    let opts = Opts::from_args();
 
     let mut lines: Vec<String> = stdin()
         .lock()
         .lines()
         .collect::<io::Result<Vec<String>>>()
         .context("could not read lines from stdin")?;
 
-    lines.par_sort_by_key(|candidate| levenshtein(target, candidate));
+    lines.par_sort_by_key(|candidate| levenshtein(&opts.target, candidate));
 
     let mut out = BufWriter::new(stdout());
     for candidate in lines {