From trait
From is Rust’s standard-library trait for infallibly converting a value of one type into another type.
Rust Servers, Services, and Apps
From is the Rust standard-library trait for defining infallible conversions from one type into another.
- How it is used
- Converts HTTP request data, response structures, wrapped JSON inputs, and distinct errors across server-side type boundaries.
- How deep it goes
- Works through concrete From implementations and unit tests, then outlines error conversion without showing its implementation.
- Examples
- Tests GET and HTTP/1.1 conversions, serializes a 404 response, and unwraps an Actix Web JSON input model.
- What you can do after
- Build it from scratch for request parsing and response serialization; apply it in Actix Web model and error workflows.
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Rust in Action: Systems programming concepts and techniques
From is a Rust standard-library trait for infallibly converting a value of one type into another type.
- How it is used
- Uses From to support value conversions and to bring multiple upstream error types into one wrapper error type.
- How deep it goes
- Works through bidirectional numeric implementations and separate error-wrapper implementations, including how the latter remove repeated map_err calls.
- Examples
- Shows Q7 conversions with f64 and f32, wrapper conversions for I/O and address-parsing errors, and NTP timestamp conversions.
- What you can do after
- Build it from scratch by implementing From for numeric types or wrapper errors, then use from(), into(), or ? where appropriate.
Read how Rust in Action: Systems programming concepts and techniques explains From trait →
Code Like a Pro in Rust
From is a Rust standard-library trait for infallible conversion from one type into another type.
- How it is used
- Standardizes conversions between types, especially converting I/O or SQLx errors into an application’s Result error type.
- How deep it goes
- Defines the trait signature and works through wrapper and custom-error implementations, including a missing-implementation compiler diagnostic.
- Examples
- Shows a string wrapper, file-reading errors, and SQLx queries using `.map_err(Into::into)`.
- What you can do after
- Build it from scratch by implementing From for a wrapper or custom error, then use it with `?` or `map_err`.
Learn Rust in a Month of Lunches
The From trait defines conversion of one Rust type into another specified type.
- How it is used
- Uses explicit conversions to connect standard-library types and give custom types convenient construction syntax.
- How deep it goes
- Explains the conversion rule, standard-library examples, custom implementations, blanket relationships, and the orphan-rule boundary.
- Examples
- Demonstrates array, string, byte-vector, City, Country, BTreeMap, and error conversions.
- What you can do after
- Build it from scratch by implementing conversions for custom types and invoking them with From::from or Into.
Read how Learn Rust in a Month of Lunches explains From trait →
Related concepts
- traitkind of · A trait is a type-level construct that defines reusable behavior or members that types can implement or compose.
- map_err methodalternative to · In Rust, map_err is a Result method that transforms an error value while leaving a successful value unchanged.
- Intoproduces · Into is Rust’s standard-library trait for infallibly converting a value into a specified target type.
- TryFromalternative to · TryFrom is a Rust standard-library trait for fallible conversion between types, returning a result that indicates success or failure.
- blanket implementationimplemented by · A blanket implementation is a generic trait implementation that applies to every type satisfying specified trait bounds.
- vectorimplements · A vector is an ordered, indexed sequence of elements, often numerical, represented as a mathematical quantity or a computational collection.
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