Lib.rs

If you have an iterator of Results, you can collect and unwrap all values into a Vec on success or return the first Err on failure:

let content_of_files = file_names.iter()
    .map(std::fs::read_to_string)
    .collect::<Result<Vec<_>, _>>()?;

The type hint in .collect makes it construct a Result instead of just a Vec. If it was .collect::<Vec<_>>() instead, it would make a Vec<Result<String, Error>> of mixed Ok and Err values.

.collect can make anything that implements FromIterator, and there are implementations of FromIterator for Result, Option, and even ().

See it in the Rust Playground.