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Quick Guide To Error Handling In Rust

Last Updated On Sunday, Apr 9, 2023 | Written By - Mudit Jain


Quick Guide To Error Handling In Rust

Rust web development provides many capabilities for dealing with instances in which something goes wrong since errors are given in the software. Rust often demands that you recognize the potential for a mistake and act before you can build your code.

This requirement applies more resilience by guaranteeing you'll find errors and manage them properly before releasing your code to production!

Rust divides errors into recoverable and unrecoverable, the two main kinds. Suppose there is a recoverable issue, like a file not found error.

In that case, we probably only want to let the user know and try the task again. We want to halt the application immediately since unrecoverable errors are usually signs of flaws, such as trying to reach a point beyond the end of an array. This might also defy the rust invalid connection protocol.

Most programming languages treat these two types of errors the same way, handling them both via techniques like exceptions.

There are no exceptions in Rust. Instead, it contains panic! A macro that halts execution when an unrecoverable error occurs and the type ResultT, E> for recoverable failures.

Before moving on to returning values from ResultT, E>, we'll also consider factors when selecting whether to try to recover from errors or halt execution.

Definition and Boxing of Errors

You may sometimes simplify the code by replacing all the many faults with a single error. It will show this using a unique error.

We can create our error types using Rust. A "good" error type often refers to several mistakes of the same kind and always meets rust exceptions.

It provides the user with attractive error messages. Additionally, it is simple to compare it to other kinds.

Good: "Please use a vector with at least one element." to owned() and

Bad: "Err(EmptyVec)." This may save information about the error, either positive or bad: Err("+ cannot be used here." to owned()) or Err(BadChar(c, position)).

Boxing Errors allow you to create shortcodes while keeping the original faults intact. The flaw is that because it is not statically specified, the underlying error type is only known at runtime.

Box supports conversion from any class that implements the Error trait into the trait object BoxError>, using From, a feature provided by the standard library to aid in boxing our errors.

Example of Handling Generic Errors

Custom rust error handling may be awkward if you cannot employ the question-mark operator. We must produce a result that can take any error to be happy.

All mistakes embody the standard:: attribute. Any mistake may become a BoxError> since all errors transform to error::Error. You can check out this example of rust error handling

Rust may determine that parse should convert to i32 based on the return type.

That leaves one question mark for the conversion issue and two question marks for the i/o problems (can't open a file or can't read as a string). Finally, we apply Ok, to the outcome.

Since our applications will have application-specific error situations, we must develop our error type. The fundamental conditions are simple:

Use Debug

You must use Display

Implementing Error

A statement describing or referring to a database item other than a table, view, index, column, or cursor could not be found or recognized.

This is true of database operations, grants or permissions, rules, and other objects.

It becomes laborious to type ResultT,MyError>, thus many Rust modules define their own Result; for instance, io::ResultT> is short for ResultT,io::Error>.

The particular error that occurs when you cannot translate a string into a floating-point number must be handled in the following example.

The way that? operates right now is to search for a conversion from the expression's error to the error that must be returned.

And the From characteristic illustrates this change. Because it implements From for all types implementing Error, Boxing errors operate as it does.

Problem with employing a generic error data type

The biggest issue with utilizing generic error types is that they make it difficult to identify particular error kinds during compilation.

This implies that only at runtime can these mistakes be found.

It can deny an operation because the user lacked the necessary authorizations or privileges; the process was prohibited (for instance, to a specific time of day), and the action was applied at the incorrect moment or in the wrong mode.

A request couldn't be fulfilled given the transaction's current condition. For instance, update requests may have been sent in a read-only transaction or sent a request either within or outside a transaction inappropriately.

Abuse of the cardinalities. This often happens when a singleton select request yields more than one row or when a nested sub-query yields an incorrect number of rows. An attempt was made to return either more or fewer rows than accepted.

Failure of serialization (Deadlock). It declined the query because of an error (for instance, a deadlock, timeout, forced abort, or an entire log file).

Except in the event of a timeout, a refused transaction is rolled back. Resubmitting the inquiry or transaction is possible. In the SQLCA structure, look for SQLWARN6.


In conclusion, "Box" the mistakes if you need to describe a general error. The Boxdyn std::error::Error> will often work to produce a general error.

Generic errors are an intelligent approach to keeping your code simple. It helps avoid needing additional boilerplate, such as matching patterns to return a standard error type or creating a custom error type. It may rapidly add a few lines of code to handle failures and rust access violation.


Eisele Candace has 7 years of experience as a freelance technical writer, specializing in content related to IT technologies, programming and UI/UX design.

Holder of a Master's degree in Journalism and Public Relations. She has also completed design and programming courses in "UI / UX design", iOS and Python in Mansfield, OH. She has been already learning Rust programming language for a year.

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