Structs in rust

Structs

struct is custom data type that lets you package together and name multiple related values that make up a meaningfull group.

Defining Structs

structs are defining in the following way.

struct User {
    active: bool,
    username: String,
    email: String,
    sign_in_count: u64,
}

Instantiating Structs

Structs are instantiated by creating an instance of the struct with the concrete values.

let user1 = User {
    active: true,
    username: String::from("sherlock"),
    email: Sting::from("sherlock@yahoo.com"),
    sign_in_count: 1,
};

Accessing Struct Values

We use dot notation to access the specific value from the struct.

user1.email // sherlock@yahoo.com

Modifying The Struct

To change the value of struct first we need make user instance as mutable. let mut user1 = User {...}.

we use the same dot notion to mutate the struct.
user1.email = String::from("jhon@yahoo.com").

Field Init Shorthand

When function parameters are passed down to the struct defnition there posiblitly repeating field names and function paramters. let say we have
funciton:

function build_user(username: String, email: string) -> User {
    //This is called implicit return.
    User {
        active: true,
        username: username,
        email: email,
        sign_in_count: 1,
    }
}

AS u see we are repeating paramters and fields here.
With help of Field Init Shorthand we can write as follows

function build_user(username: String, email: string) -> User {
    //This is called implicit return.
    User {
        active: true,
        username,
        email,
        sign_in_count: 1,
    }
}

Creating new instances from other instance with Struct Update Syntax(Spread syntax if you know JS).

let user2 = User {
    email: String::from("holmes@yahoo.com");
    ...user1
};
It will have same the values of user1 and but email will be different.

Structs can be defined without the name and value fields.

struct Color(i32, i32, i32);
struct Point(i32, i32, i32);

Structs can also be defined unit-like without any field or types.

struct AlwaysEqual;

When to use structs

We use struct when we want to convey the meaning of our data in our code.

for example:
let say i have tuple like this

let rect1 = (30, 50)

which does not convey the what the values represent. In this case we can use struct to define our values with right structure.

let rect1 = Rectangle {
    width: 30,
    height: 50,
};
and the struct is 
struct Rectangle {
    width: u32,
    height: u32,
}