extern crate csv;
extern crate serde;
#[macro_use]
extern crate serde_derive;
use std::env;
use std::error::Error;
use std::io;
use std::process;
// Unlike previous examples, we derive both Deserialize and Serialize. This
// means we'll be able to automatically deserialize and serialize this type.
#[derive(Debug, Deserialize, Serialize)]
#[serde(rename_all = "PascalCase")]
struct Record {
city: String,
state: String,
population: Option<u64>,
latitude: f64,
longitude: f64,
}
fn run() -> Result<(), Box<Error>> {
// Get the query from the positional arguments.
// If one doesn't exist or isn't an integer, return an error.
let minimum_pop: u64 = match env::args().nth(1) {
None => return Err(From::from("expected 1 argument, but got none")),
Some(arg) => arg.parse()?,
};
// Build CSV readers and writers to stdin and stdout, respectively.
// Note that we don't need to write headers explicitly. Since we're
// serializing a custom struct, that's done for us automatically.
let mut rdr = csv::Reader::from_reader(io::stdin());
let mut wtr = csv::Writer::from_writer(io::stdout());
// Iterate over all the records in `rdr`, and write only records containing
// a population that is greater than or equal to `minimum_pop`.
for result in rdr.deserialize() {
// Remember that when deserializing, we must use a type hint to
// indicate which type we want to deserialize our record into.
let record: Record = result?;
// `map_or` is a combinator on `Option`. It take two parameters:
// a value to use when the `Option` is `None` (i.e., the record has
// no population count) and a closure that returns another value of
// the same type when the `Option` is `Some`. In this case, we test it
// against our minimum population count that we got from the command
// line.
if record.population.map_or(false, |pop| pop >= minimum_pop) {
wtr.serialize(record)?;
}
}
// CSV writers use an internal buffer, so we should always flush when done.
wtr.flush()?;
Ok(())
}
fn main() {
if let Err(err) = run() {
println!("{}", err);
process::exit(1);
}
}