Default
Default is a Rust standard-library trait that defines how to construct a type’s default value.
Learn Rust in a Month of Lunches
Default is the Rust standard trait that defines how to construct a default value for a type.
- How it is used
- Provides a common starting value for custom types and for operations that require the `Default` trait.
- How deep it goes
- Works through standard defaults, a manual implementation, derivation, and partial struct construction.
- Examples
- Uses integers, strings, booleans, custom structs, a calculator enum, and a value replaced through `std::mem::take`.
- What you can do after
- Build it from scratch with a manual implementation, or apply `#[derive(Default)]` when the type’s fields support it.
Read how Learn Rust in a Month of Lunches explains Default →
Write Powerful Rust Macros
Default is the standard Rust trait for constructing a default value of a type.
- How it is used
- Uses Default as a fallback for omitted builder fields instead of immediately panicking.
- How deep it goes
- Explains trait usage, generated unwrap_or_default calls, and field-specific diagnostics, but does not develop custom Default implementations.
- Examples
- Demonstrates defaulted String and integer fields, a non-Default field failure, and generated quote_spanned assertions.
- What you can do after
- Apply it via Rust builders and generated code to supply fallback values and enforce Default bounds at compilation.
Related concepts
- absolute pathused by · An absolute path is a Rust path that identifies an item from a crate or other root namespace through complete namespace qualification.
- derive macroimplemented by · A Rust derive macro is an attribute that automatically generates implementations of specified traits or related functionality for a type.
- HTTP responseconfigured by · An HTTP response is a protocol message sent by a server to a client after an HTTP request, containing status information, headers, and optionally a body.
These guides are generated from the text of Manning books by Manning's knowledge graph and link to the sections they draw on. The full books are available on liveBook and at manning.com.