CODEWITHSUNDEEP
rust
Rajeev Ranjan
Rajeev Ranjan

Reputation: 4076

How do I ignore an error returned from a Rust function and proceed regardless?

When it is known that some piece of code might throw an error, we make use of try/catch blocks to ignore such errors and proceed. This is done when the error is not that important but maybe we only want to log it:

try{
    int i = 1/0;
} catch( ArithmeticException e){
    System.out.println("Encountered an error but would proceed.");
} 
x = y;

Such a construct in Java would continue on to execute x = y;.

Can I make use of match to do this or any other construct?

I do see a try! macro, but perhaps it would return in case of an error with the return type of the method as Result.

I want to use such a construct in a UT to ensure it continues to run even after an error has occurred.

Upvotes: 53

Views: 47278

Answers (1)

Tim Diekmann
Tim Diekmann

Reputation: 8466

Functions in Rust which can fail return a Result:

Result<T, E> is the type used for returning and propagating errors. It is an enum with the variants, Ok(T), representing success and containing a value, and Err(E), representing error and containing an error value.

I highly recommend reading the Error Handling section in the Rust Book:

Rust has a number of features for handling situations in which something goes wrong

If you want to ignore an error, you have different possibilities:

  • Don't use the Result:

      let _ = failing_function();

    The function will be called, but the result will be ignored. If you omit let _ = , you will get a warning. As of Rust 1.59, you can omit the let and just write _ = failing_function();.

  • Ignore the Err variant of Result using if let or match:

      if let Ok(ret) = failing_function() {
      // use the returned value
  }

    You may also convert the Result into Option with Result::ok:

      let opt = failing_function().ok();

  • Unwrap the error. This code panics if an error occurred though:

      let ret = failing_function().unwrap();
  // or
  let ret = failing_function().expect("A panic message to be displayed");

try!() unwraps a result and early returns the function, if an error occurred. However, you should use ? instead of try! as this is deprecated.

See also:

Upvotes: 87

Related Questions