Introducing traits in Rust - what they are and how to use them

Introduction to Rust’s Traits

Section Overview: In this section, the speaker introduces the topic of Rust’s traits and explains what they are. They also mention that they will demonstrate how to use them and explore their role within the Rust programming language.

What is a Trait?

  • A trait is an abstract interface or an abstract base class in object-oriented languages.
  • It allows us to define functions and function signatures.
  • It can be implemented by multiple types.

Basic Rust Program

Section Overview: In this section, the speaker demonstrates a simple Rust program and explains how functions work in Rust.

Creating Functions in Rust

  • Functions can be defined with parameters and return values.
  • The difference between &str and String data types is not explained at this point.
  • Functions can be called from the main function using arguments passed as parameters.

Abstraction with Traits

Section Overview: In this section, the speaker discusses how traits allow for abstraction in Rust programming.

⭐️Using Traits for Abstraction

  • Repeatedly creating functions can become tedious.
  • Traits provide a way to create abstractions that can be used across multiple types.
  • This allows for more efficient code writing and easier maintenance.

Defining Traits in Rust

Section Overview: In this section, the speaker delves deeper into defining traits in Rust programming.

Defining Traits

  • A trait defines a set of methods that a type must implement.
  • Types implementing a trait must provide implementations for all its methods.
  • A struct can implement multiple traits.

# Implementing Traits in Rust

Section Overview: In this section, the speaker explains how to implement traits in Rust and why they are useful.

Implementing Score Method for String Type

  • The speaker receives an error message that they need to implement a method called “score” for a string type.
  • They change the code to refer to “self” instead of the string type.
  • The speaker implements the score method for the string type by creating a new method.
  • They explain that implementing traits allows us to define an interface and give any type its own new method.

⭐️Why Use Traits?

  • The speaker answers a question about why we bother with traits when we already had a free function called score. They explain that traits become useful when defining an interface or working with generics.
  • They give an example of wanting to report on any type using a generic function and ensuring that each type has some sort of score.
  • The speaker explains how traits allow us to parameterize functions and work within the generics system.

Implementing Score Method for Other Types

  • The speaker demonstrates how we can implement the score method for other types such as i32.

# Introduction to Rust Traits

Section Overview: In this section, the speaker introduces Rust traits and explains how they can be used to define or bring together functionalities that are common across types.

⭐️Operator Overloading with Traits

  • Operator overloading is implemented with traits in Rust.
  • To implement operator overloading, a trait (e.g., add trait) must be implemented, and the right-hand side of the operation must be of the same type.

Iteration with Traits

  • Types that implement the IntoIterator trait can be used with Rust’s for loop syntax.
  • Many syntaxes in Rust are compiled down to trait implementations, making it important to become familiar with core traits.

# Implementing a Shape Trait in Rust

Section Overview: In this section, the speaker discusses how to implement a shape trait in Rust using examples.

Defining a Shape Trait

  • A shape trait can be defined to require an area function to be defined for each shape.
  • A 2D shape has height and width parameters and an area method.

Parameterizing Types

  • Types such as scalar can be parameterized as any single type as long as they’re the same.

Implementing Methods for Square Shape

  • To implement methods for square shapes, three methods need to be defined - height, width, and area.
  • s The height and width functions are defined as the same for a square shape.
  • A default implementation can be defined for the area method.

Implementing Traits in Rust

Section Overview: In this section, the speaker implements a 2D square and demonstrates how to fall back to default implementations for other methods using traits. They also discuss the challenges of understanding and working with standard library traits.

Implementing a 2D Square

  • To implement multiplication, the speaker creates a type that must implement multiplication.
  • The speaker needs another block for their implementation.
  • They create a static method on square new that returns type self, which refers back to the original type. They then set its height as f32.
  • The speaker creates a square by calling the static method square new and giving it a height value.
  • They print line square and area. Although they haven’t defined area themselves inside their implementation block, they are falling back to the default implementation.

Falling Back to Default Implementations

  • The speaker encounters an issue where they need to restrict scalar to a type that is able to be multiplied.
  • They add a type bound but encounter rebound mismatched types error because of the return type.
  • To get it to pass, they remove the type parameterization and will look up syntax later.
  • The area is correct irrespective of unit because of trait implementation.

Understanding Standard Library Traits

  • There are dozens of standard library traits making it difficult to understand where one should begin or how they all fit together.
  • The speaker provides some brief insight into understanding standard library traits.

# Understanding Debug and Display Traits

Section Overview: In this section, the speaker explains how to use the debug and display traits in Rust programming.

Implementing Debug Trait

  • The derive annotation instructs the Rust compiler to automatically implement a debug trait for custom types.
  • Debug can only be implemented if your custom type uses types that also implement debug.
  • If a custom type is changed, such as adding a new struct, then derived debug will no longer work.

Implementing Display Trait

  • Display is designed for output intended for users rather than programmers.
  • Unlike debug, display has no default implementation and must be implemented manually.
  • The formatter is an internal type to the format module which can be ignored when starting out with Rust programming.

Customizing Output with Display Trait

  • The thing being printed has a lifetime that must be long enough for the print to finish.
  • We can describe how we want to display our custom type using the format! macro.

# Implementing Traits in Rust

Section Overview: In this section, the speaker discusses implementing traits in Rust and how to familiarize oneself with them.

Familiarizing Oneself with Traits

  • The speaker suggests that one should start by familiarizing themselves with the Debug and Display traits.
  • The next trait to learn is iteration, which is slightly more complicated.

⭐️Iteration Trait

  • The speaker explains that iteration requires multiple computers to be created.
  • Traits are important for iteration, as well as for the size of each element of an array.
  • There are two important types of traits for iteration - Iterator and IntoIterator.
  • The speaker demonstrates how to implement the IntoIterator trait for a structure containing random numbers.

Printing to Screen

  • The speaker defines the type item as usize and demonstrates how to print random numbers using iterators.
  • He then shows how to take five random numbers using the take() method on iterators.

Conclusion

  • After learning about debug display and iteration, understanding the distinction between them is crucial.

# Rust Traits

Section Overview: In this section, the speaker talks about Rust traits and how they work.

Understanding Enums

  • An enum is either the non-variant or sum of type t.
  • Return self seed.

Changing Random Numbers

  • Change the seed to 10.
  • The output should be 50 50 50.
  • A set of random numbers can be empty, and nothing will be printed out.

Learning Traits

  • Display debug iteration is where to start learning traits.
  • Operator overloading traits are also important to learn.

Reading Documentation

  • Look at implementations to find out what methods you can use on a type.
  • Partial equality is the trait that supports the equal sign operator.
  • Paths can be equal to an OS string or path buffers.

# Double Equals and Deref Trait

Section Overview: In this section, the speaker talks about the use of double equals in Rust and demonstrates how types can implement methods that they don’t actually implement using the Deref trait.

Double Equals

  • Double equals can be used for a lot of things in Rust.

⭐️Deref Trait

  • The Deref trait enables a type to masquerade as another type and convert itself into that type.
  • This allows a type to implement methods that it doesn’t actually implement by calling those methods on the converted type.
  • The Deref trait is used implicitly by the compiler in many circumstances through drift coercion, which means that the dereference operation coerces to another type.
  • Rust provides ergonomics through implicit use of the Deref trait, but it can be confusing if you are expecting everything to be explicit.

⭐⭐⭐️️️Traits and Associated Types

Section Overview: In this section, the speaker discusses traits and associated types in Rust. They explain what a trait is, when to use an associated type, and provide some useful documentation for further learning.

What are Associated Types?

  • An associated type is a type that is defined within a trait.
  • It can be used to define a scalar value within an object.
  • It’s useful if you want to include an associated type with inside a generic type argument or parameter so that implementers can choose which type they want to return.

When Should You Use Associated Types?

  • The speaker asks the audience when they think it’s appropriate to use an associated type.
  • If it’s not required, you can safely ignore it.
  • The Rust reference provides more technical information on traits and their implementation.

Other Useful Documentation

  • The Rust reference is a good guide for understanding how Rust works.
  • The Rust by Example chapter on traits provides another definition of traits that may be useful for beginners.

Rust by Example: Traits and Generics

Section Overview: In this section, the speaker discusses the definition of traits in Rust and how they relate to generics. They also explain why some traits have no methods and are used as marker traits.

Definition of Traits

  • The definition of a trait in Rust is too loose.
  • The speaker objects to this definition.

⭐️Sync Trait

  • The Sync trait has no methods at all and is a marker trait.
  • It indicates to the type system about some property which matters to you as a programmer, such as concurrency.
  • There’s no magical annotation on your type for implementing Sync.
  • It’s just an assertion that you provide as a programmer to the compiler.

⭐️Marker Traits

  • Marker traits are used when there is no need for any associated information with the trait.
  • Rust by example asserts that a trait is a collection of methods, but important traits exist where that’s not true.

Conclusion

  • The speaker appreciates people’s participation and questions.
  • They encourage connecting with them on Twitter or asking questions in the comments.
  • A tutorial will be created based on this discussion.

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