Result type
A type that represents an operation’s outcome as either a successful value or a failure value.
Write Powerful Rust Macros
Result is the Rust standard-library enum representing either successful output or an error value.
- How it is used
- Makes expected failure explicit while replacing selected panic paths in a procedural macro.
- How deep it goes
- Explains Result through sum types, return rewrites, tests, generated-code debugging, and syn::Error integration, while leaving transformations intentionally partial.
- Examples
- Uses a custom Either, person creation validation, Result-returning macro targets, empty panic calls, and happy- and unhappy-path tests.
- What you can do after
- Build it from scratch by rewriting simple function signatures, success values, and selected panic branches into Result-based code.
Rust Servers, Services, and Apps
A Result is a Rust standard-library generic type representing either successful output or an error.
- How it is used
- Supports recoverable-failure returns in Rust functions and methods, including TCP operations and web-server startup.
- How deep it goes
- Defines success and error values, demonstrates `unwrap` and `?`, and summarizes combinators and conversions without detailing their implementation.
- Examples
- Uses `unwrap` on TCP bind, connect, read, and write operations, and shows `?` in an Actix server’s `main` function.
- What you can do after
- Apply it via Rust function signatures to return success values or errors and propagate failures with `?`.
Read how Rust Servers, Services, and Apps explains result type →
Refactoring to Rust
Result is Rust's standard-library enum representing either success with an Ok value or failure with an Err value.
- How it is used
- Represents success or failure from functions that might fail, keeping errors separate from normal return values.
- How deep it goes
- Defines both enum variants and works through matching, propagation with `?`, and error conversion with `map_err`.
- Examples
- Uses negative FizzBuzz input, parallel `match` and `?` functions, and lowercase and uniqueness checks for usernames.
- What you can do after
- Apply it via Rust’s standard-library `Result` to handle, forward, and transform function errors.
Rust in Action: Systems programming concepts and techniques
Result is Rust's standard result type that contains either a successful value or an error value.
- How it is used
- Marks operations that may fail, especially file methods, with either a successful value or an error message.
- How deep it goes
- Defines Ok and Err and demonstrates return signatures and unwrap(), while deferring more sophisticated error handling.
- Examples
- Uses file-opening and reading methods, a u16-to-i32 conversion, and a time-setting operation.
- What you can do after
- Build it from scratch: give potentially failing file methods Result return types and recognize why unwrap() is risky.
Read how Rust in Action: Systems programming concepts and techniques explains result type →
Learn Rust in a Month of Lunches
Result is a Rust enum type representing either a successful value or an error from an operation that may fail.
- How it is used
- Represents an operation that may succeed or fail, with a value for either outcome.
- How deep it goes
- Explains variants, generic payloads, simple handling, and compiler feedback; uses String errors without defining a formal error type.
- Examples
- Shows a number-checking function returning Ok or a String error, plus a compiler warning for an ignored Result.
- What you can do after
- Build it from scratch: return Ok or Err from a simple function and check the outcome instead of ignoring it.
Read how Learn Rust in a Month of Lunches explains result type →
F# in Action: A Revised Edition of Get Programming with F#
A result type represents either a successful value or an error value, allowing an operation to return validation failures without raising an exception.
- How it is used
- Models validation and other expected failures as explicit return values carrying error information.
- How deep it goes
- Defines Ok and Error payloads, demonstrates customer validation, and extends failures to multiple error values.
- Examples
- Uses raw-customer conversion, aggregated validation messages, and JSON-to-domain validation for web endpoints.
- What you can do after
- Apply it via F# Result values to return validation errors, branch on outcomes, and map failures to HTTP responses.
Read how F# in Action: A Revised Edition of Get Programming with F# explains result type →
Idiomatic Rust
Result is Rust's standard-library enum representing either successful output of type T or an error of type E.
- How it is used
- Uses `Result` to propagate file-operation errors and retain or separate outcomes of string parsing.
- How deep it goes
- Works through matching, `?`, error conversion, and iterator handling; does not examine the enum’s implementation.
- Examples
- Shows file creation and writing, custom error wrapping, and partitioning parsed strings into successes and failures.
- What you can do after
- Apply it via `?` and `match` to handle failures, and use `partition()` when parsing errors must remain visible.
Code Like a Pro in Rust
Result is a Rust enum representing either successful computation with a value or failure with an error.
- How it is used
- Carries success values or errors through function return paths, especially for fallible operations such as I/O.
- How deep it goes
- Shows the enum variants and works through error propagation, custom errors, and conversions without exploring enum internals.
- Examples
- Demonstrates reading a file with `?`, converting I/O errors, and returning file contents as a `Result`.
- What you can do after
- Apply it to return fallible results, propagate I/O errors, and convert errors into a crate-specific type.
Related concepts
- enumkind of · An enum is a type or language construct whose values are selected from a finite set of named alternatives, which may carry associated data.
- union typekind of · A union type is a type whose values can be any one of several specified alternative types or variants.
- panicalternative to · A panic is a runtime failure mechanism that abruptly stops ordinary execution when an unrecoverable error or violated assumption prevents safe continuation.
- question mark operatorused by · The question mark operator is Rust postfix syntax that propagates an error or absence by returning early and otherwise produces the successful value.
- exceptionused by · An exception is a runtime signal or object representing an abnormal condition that interrupts ordinary program flow and may be handled or propagated.
- unwrapused by · unwrap is a Rust method that extracts a value from an Option or Result and panics when it is absent or represents an error.
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