67 lines
1.7 KiB
Markdown
67 lines
1.7 KiB
Markdown
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% Ergonomic error handling
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Error propagation with raw `Result`s can require tedious matching and
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repackaging. This tedium is largely alleviated by the `try!` macro,
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and can be completely removed (in some cases) by the "`Result`-`impl`"
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pattern.
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### The `try!` macro
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Prefer
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```rust
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use std::io::{File, Open, Write, IoError};
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struct Info {
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name: String,
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age: int,
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rating: int
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}
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fn write_info(info: &Info) -> Result<(), IoError> {
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let mut file = File::open_mode(&Path::new("my_best_friends.txt"),
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Open, Write);
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// Early return on error
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try!(file.write_line(format!("name: {}", info.name).as_slice()));
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try!(file.write_line(format!("age: {}", info.age).as_slice()));
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try!(file.write_line(format!("rating: {}", info.rating).as_slice()));
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return Ok(());
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}
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```
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over
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```rust
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use std::io::{File, Open, Write, IoError};
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struct Info {
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name: String,
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age: int,
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rating: int
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}
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fn write_info(info: &Info) -> Result<(), IoError> {
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let mut file = File::open_mode(&Path::new("my_best_friends.txt"),
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Open, Write);
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// Early return on error
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match file.write_line(format!("name: {}", info.name).as_slice()) {
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Ok(_) => (),
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Err(e) => return Err(e)
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}
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match file.write_line(format!("age: {}", info.age).as_slice()) {
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Ok(_) => (),
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Err(e) => return Err(e)
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}
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return file.write_line(format!("rating: {}", info.rating).as_slice());
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}
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```
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See
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[the `result` module documentation](http://static.rust-lang.org/doc/master/std/result/index.html#the-try!-macro)
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for more details.
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### The `Result`-`impl` pattern [FIXME]
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> **[FIXME]** Document the way that the `io` module uses trait impls
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> on `IoResult` to painlessly propagate errors.
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