problem in reading fgb file

[orkun]

Hi,
I tried to reaf a fgb file as ``` use flatgeobuf::*;
use std::fs::File;
use std::io::BufReader;

fn main() {
let mut filein = BufReader::new(File::open("countries.fgb")?);
let mut fgb = FgbReader::open(&mut filein)?.select_all()?;
while let Some(feature) = fgb.next()? {
println!("{}", feature.property::("name").unwrap());
println!("{}", feature.to_json()?);
}
}```. cargo build says:

Compiling geo1 v0.1.0 (/usr/local/geo1)
error[E0277]: the ? operator can only be used in a function that returns Result or Option (or another type that implements FromResidual)
--> src/main.rs:6:64
|
5 | fn main() {
| --------- this function should return Result or Option to accept ?
6 | let mut filein = BufReader::new(File::open("countries.fgb")?);
| ^ cannot use the ? operator in a function that returns ()
|
= help: the trait FromResidual<Result<Infallible, std::io::Error>> is not implemented for ()

error[E0277]: the ? operator can only be used in a function that returns Result or Option (or another type that implements FromResidual)
--> src/main.rs:7:47
|
5 | fn main() {
| --------- this function should return Result or Option to accept ?
6 | let mut filein = BufReader::new(File::open("countries.fgb")?);
7 | let mut fgb = FgbReader::open(&mut filein)?.select_all()?;
| ^ cannot use the ? operator in a function that returns ()
|
= help: the trait FromResidual<Result<Infallible, flatgeobuf::Error>> is not implemented for ()

error[E0277]: the ? operator can only be used in a function that returns Result or Option (or another type that implements FromResidual)
--> src/main.rs:7:61
|
5 | fn main() {
| --------- this function should return Result or Option to accept ?
6 | let mut filein = BufReader::new(File::open("countries.fgb")?);
7 | let mut fgb = FgbReader::open(&mut filein)?.select_all()?;
| ^ cannot use the ? operator in a function that returns ()
|
= help: the trait FromResidual<Result<Infallible, flatgeobuf::Error>> is not implemented for ()

error[E0277]: the ? operator can only be used in a function that returns Result or Option (or another type that implements FromResidual)
--> src/main.rs:8:41
|
5 | fn main() {
| --------- this function should return Result or Option to accept ?
...
8 | while let Some(feature) = fgb.next()? {
| ^ cannot use the ? operator in a function that returns ()
|
= help: the trait FromResidual<Result<Infallible, flatgeobuf::Error>> is not implemented for ()

error[E0599]: no method named to_json found for reference &FgbFeature in the current scope
--> src/main.rs:10:32
|
10 | println!("{}", feature.to_json()?);
| ^^^^^^^ method not found in &FgbFeature

Some errors have detailed explanations: E0277, E0599.
For more information about an error, try rustc --explain E0277.
error: could not compile geo1 (bin "geo1") due to 5 previous errors ```

[lnicola]

You should probably use https://docs.rs/anyhow/latest/anyhow/ and change the signature of main to fn main() -> anyhow::Result<()>. You'll also need to add an Ok(()) line at the end.

https://doc.rust-lang.org/book/ch09-02-recoverable-errors-with-result.html has more info.