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//! Provides a trait for `std::io::Result` that adds a method making
//! it easy to tell the difference between a file not found and
//! another error, since a common practice is to handle a file if it
//! exists.
//!
//! # Examples
//! ````
//! use io_result_optional::IoResultOptional;
//! use std::fs::File;
//! # use std::io;
//!
//! # fn readconfig(data: File) -> u8 {
//! # 17
//! # }
//! # fn main() -> io::Result<()> {
//! let config = File::open(".app.rc")
//! .optional()?
//! .map(readconfig)
//! .unwrap_or_default();
//! # Ok(())
//! # }
//! ````
//!
//! ````
//! use io_result_optional::IoResultOptional;
//! use std::fs::File;
//! # use std::io;
//!
//! # fn main() -> io::Result<()> {
//! if let Some(input) = File::open("data").optional()? {
//! // The data exists, so handle it ...
//! // If it doesn't exist, it is just ignored
//! // If there is another error, this function returns it.
//! }
//! # Ok(())
//! # }
//! ````
use std::io;
/// A trait for [`io::Result`] that adds a method making it easy to
/// tell the difference between a file not found and another error,
/// since a common practice is to handle a file if it exists.
pub trait IoResultOptional<T> {
/// Consider the given file access optional.
/// if the result is an error with [`io::ErrorKind`] `NotFound`, convert it to
/// `Ok(None)`.
/// If it is any other error, return it as-is,
/// and if it is `Ok(value)` convert it to `Ok(Some(value))`.
///
/// # Examples
/// ````
/// use std::fs::File;
/// # use std::io;
/// use io_result_optional::IoResultOptional;
///
/// # fn parseconfig(data: File) -> u8 {
/// # 17
/// # }
/// # fn main() -> io::Result<()> {
/// let config = File::open(".app.rc")
/// .optional()?
/// .map(parseconfig)
/// .unwrap_or_default();
/// # Ok(())
/// # }
/// ````
fn optional(self) -> io::Result<Option<T>>;
}
impl<T> IoResultOptional<T> for io::Result<T> {
fn optional(self) -> io::Result<Option<T>> {
match self {
Ok(value) => Ok(Some(value)),
Err(ref e) if e.kind() == io::ErrorKind::NotFound => Ok(None),
Err(e) => Err(e),
}
}
}
#[cfg(test)]
mod tests {
use crate::IoResultOptional;
use std::fs::File;
use std::io;
use std::path::Path;
#[test]
fn existing_some() {
assert!(
File::open(&Path::new(env!("CARGO_MANIFEST_DIR")).join("Cargo.toml"))
.optional()
.unwrap()
.is_some()
)
}
#[test]
fn non_existing_none() {
assert!(
File::open(&Path::new(env!("CARGO_MANIFEST_DIR")).join("nosuch.file"))
.optional()
.unwrap()
.is_none()
)
}
#[test]
fn other_is_error() {
let result: io::Result<()> = Err(io::Error::new(io::ErrorKind::TimedOut, "too slow"));
assert_eq!(
format!("{:?}", result.optional()),
"Err(Custom { kind: TimedOut, error: StringError(\"too slow\") })",
)
}
}