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Add notes on expect metorhod for error handling

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Marcello 2021-11-20 10:45:24 +01:00
parent 4817b5b939
commit c31ef640a8
1 changed files with 4 additions and 1 deletions
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5
Rust/Rust.md
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@ -777,6 +777,7 @@ result.unwrap_or(value); // get value of OK or return a specified value
result.unwrap_or_default(); // get value of Ok or return the default value of T result.unwrap_or_default(); // get value of Ok or return the default value of T
result.unwrap_err(); // get value of Err or panic if Ok result.unwrap_err(); // get value of Err or panic if Ok
result_or_option.expect("Error Message"); // if Err or None panics with a custom error message
fn returns_result() -> Result<T, E> { fn returns_result() -> Result<T, E> {
let result = match may_return_err() { let result = match may_return_err() {
@ -789,6 +790,7 @@ fn returns_result() -> Result<T, E> {
// same as // same as
fn returns_result() -> Result<T, E> { fn returns_result() -> Result<T, E> {
let result = may_return_err()?; // error propagation let result = may_return_err()?; // error propagation
// result contains Err ot value of Ok
Ok(result) Ok(result)
} }
@ -797,7 +799,8 @@ fn returns_result() -> Result<T, E> {
Ending an expression with `?` will result in the unwrapped success (`Ok`) value, unless the result is `Err`, in which case `Err` is returned early from the enclosing function. Ending an expression with `?` will result in the unwrapped success (`Ok`) value, unless the result is `Err`, in which case `Err` is returned early from the enclosing function.
`?` can only be used in functions that return `Result` because of the early return of `Err` that it provides. `?` can only be used in functions that return `Result` because of the early return of `Err` that it provides.
*NOTE*: When `None` is used the type of `Option<T>` must be specified, because the compiler can't infer the type that the `Some` variant will hold by looking only at a `None` value. **NOTE**: When `None` is used the type of `Option<T>` must be specified, because the compiler can't infer the type that the `Some` variant will hold by looking only at a `None` value.
**NOTE**: error values that have the `?` operator called on them go through the `from` function, defined in the `From` trait in the standard library, which is used to convert errors from one type into another
### Match Expressions ### Match Expressions