Code shared from the Rust Playground

playground.rs

//! newtype patternで簡単に元の型と同等の機能を提供するには？

use itertools::Itertools;

macro_rules! impl_as {
    ($newtype:ty, $basetype:ty, $field:tt, $method:ident) => {
        impl $newtype {
            fn $method(&self) -> &$basetype {
                &self.$field
            }
        }
        
        impl AsRef<$basetype> for $newtype {
            fn as_ref(&self) -> &$basetype {
                self.$method()
            }
        }
    }
}

macro_rules! impl_borrow {
    ($newtype:ty, $basetype:ty, $field:tt) => {
        impl std::borrow::Borrow<$basetype> for $newtype {
            fn borrow(&self) -> &$basetype {
                &self.$field
            }
        }
    }
}

macro_rules! impl_deref {
    ($newtype:ty, $basetype:ty, $field:tt) => {
        impl std::ops::Deref for $newtype {
            type Target = $basetype;
            fn deref(&self) -> &$basetype {
                &self.$field
            }
        }
    }
}

#[derive(Debug, Clone)]
struct CsvLine(String);
impl_as!(CsvLine, str, 0, as_str);
impl_as!(CsvLine, std::string::String, 0, as_string);
impl_borrow!(CsvLine, str, 0);
impl_borrow!(CsvLine, std::string::String, 0);
impl_deref!(CsvLine, str, 0);

impl CsvLine {
    fn from_columns<'a, I, S>(columns: I) -> CsvLine 
    where
        S: AsRef<str> + 'a,
        I: Iterator<Item = &'a S>
    {
        CsvLine(columns.map(|s| s.as_ref()).join(","))
    }
}

fn main() {
    let columns = ["aaa", "bbb", "ccc"];
    let csv_line = CsvLine::from_columns(columns.iter());
    
    println!("{:?}", csv_line);
    println!("{}", csv_line.as_str());
    println!("{}", csv_line.as_string());
    csv_line.as_str().split(",").enumerate().for_each(|(i,c)| println!("{}: {}", i, c));
    
    let s: &str = &csv_line;
    println!("{}", s);
}