Struct show_notes::e004::struct_container::MethodDemonstrator

pub struct MethodDemonstrator {
    pub an_int: i64,
    pub a_string: String,
    a_tuple: (f64, String),
}

Shows how methods work. Elaborates only a little on the e001 examples.

Fields

an_int: i64

a_string: String

a_tuple: (f64, String)

A tuple holding a floating point value and a string slice. (We’ll discuss string slices in a future episode.)

Implementations

impl MethodDemonstrator

pub fn new() -> MethodDemonstrator

A standard constructor pattern.

You’ve seen this before, in the e001 code!

Note that Rust doesn’t have constructors in the same sense as C++ or Java: you can construct a MethodDemonstrator just as this function does somewhere else. Using new is a convenient convention, so you can just call MethodDemonstrator::new() to get an instance, rather than needing to worry about the details of the struct.

This is particularly important because not all types are necessarily public; you may not be able to construct a given struct correctly if it has hidden types, especially computed properties, which should be initialized during its construction.

pub fn method(&self)

A standard struct instance method.

Note that instance methods take a reference to self as the first argument. It needs to be a reference for normal methods, because if it isn’t, the struct instance will be moved into the function—the method will own, not just borrow—the reference, and after the method call ends, the item will be destroyed.

Of course, if you need to write a custom destructor for a more complex type, you now have a pretty good idea how to write the first argument to that method…

pub fn get_hidden_data(&self) -> (f64, String)

A getter for data which is not publicly accessible in the type.

If you try to access the tuple contents directly, e.g. with an instance of the struct outside this module, you will fail. (See the example in demonstrate_methods.)

The data can be accessed by the struct itself, however, so you can get or set the data, as here.

We use clone because we need to get not the items themselves (which we could otherwise only get as references) but their values; the clone method is from the Clone trait, which is available on many basic types in the system. Again, we will return to traits in a later episode.