TryInto

TryInto is a trait in the Rust standard library that represents fallible conversions from one type to another. It is defined in std::convert and is used for conversions that can fail at runtime, returning a Result rather than performing a guaranteed cast.

TryInto is automatically implemented for a type T when the destination type U implements TryFrom<T>. In practice, this means you can write value.try_into() to attempt a conversion to U. The method has the signature fn try_into(self) -> Result<U, Self::Error>, and it delegates to U::try_from(self).

Example:

use std::convert::TryInto;

let x: i32 = 300;

let y: Result<u8, _> = x.try_into();

If the value fits in the target type, you get Ok(v); otherwise you receive an Err with the conversion’s error type.

Error handling and usage patterns:

The error type is associated with the destination type’s TryFrom implementation, and is often something like TryFromIntError for integer conversions. You can propagate errors with the ? operator in functions that return a Result, for example:

fn to_u8(n: i32) -> Result<u8, <u8 as std::convert::TryFrom<i32>>::Error> {

let v: u8 = n.try_into()?;

Ok(v)

}

Relation to TryFrom:

TryInto is a convenient counterpart to TryFrom. If U implements TryFrom<T>, then T automatically implements TryInto<U>. This provides a symmetrical, ergonomic way to perform fallible conversions in either direction.

Compared to as:

TryInto enforces that the value actually fits in the target type and returns an error on failure, whereas the as cast may perform lossy or wraparound conversions without signaling failure. Hence TryInto is preferred when failure should be handled gracefully.

See also: TryFrom.