tryfrom

TryFrom is a trait in Rust's standard library (std::convert) that represents fallible conversions between types. It defines an associated type Error and a single method: try_from(value: T) -> Result<Self, Self::Error>. Implementing TryFrom lets a type indicate how it can be constructed from another type, with the possibility of failure returning an error instead of panicking.

TryFrom is designed to complement the infallible From/Into traits. Where From::from or Into::into produce a value without failure, TryFrom enables controlled failure. The corresponding trait TryInto provides the reciprocal operation as a method try_into(self) -> Result<T, Self::Error>. There is a standard blanket implementation that automatically provides TryInto for any type T when the target type U implements TryFrom<T>.

Common use cases include safe conversions that may overflow or otherwise be invalid, such as converting from a larger integer type to a smaller one, or converting external data into an internal representation after validation. The Error associated type may be any type; in practice it often carries information about the failure and may implement Display or Error.

Usage examples include implementing TryFrom for a custom type to enforce invariants during construction, or relying on library implementations such as TryFrom<usize> for u8, which will yield an error if the value is outside the target range. In code, you can either call TargetType::try_from(source) or source.try_into() when the target implements TryFrom for that source.