From c31ef640a8fb5847a37713c77927093e57e9b569 Mon Sep 17 00:00:00 2001 From: Marcello Lamonaca Date: Sat, 20 Nov 2021 10:45:24 +0100 Subject: [PATCH] Add notes on expect metorhod for error handling --- Rust/Rust.md | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/Rust/Rust.md b/Rust/Rust.md index 8a4e9ca..cc2fcf9 100644 --- a/Rust/Rust.md +++ b/Rust/Rust.md @@ -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_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 { let result = match may_return_err() { @@ -789,6 +790,7 @@ fn returns_result() -> Result { // same as fn returns_result() -> Result { let result = may_return_err()?; // error propagation + // result contains Err ot value of Ok Ok(result) } @@ -797,7 +799,8 @@ fn returns_result() -> Result { 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. -*NOTE*: When `None` is used the type of `Option` 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` 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