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08. primitive_data_types.md

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Primitive Data Types

  • bool : true or false
let x = true;
let y: bool = false;

// ⭐️ no TRUE, FALSE, 1, 0
  • char : a single Unicode scalar value
let x = 'x';
let y = '😎';

// ⭐️ no "x", only single quotes
//because of Unicode support, char is not a single byte, but four.
  • i8 i16 i32 i64 : fixed size(bit) signed(+/-) integer types
DATA TYPE MIN MAX
i8 -128 127
i16 -32768 32767
i32 -2147483648 2147483647
i64 -9223372036854775808 9223372036854775807

💡 Min and max values are based on IEEE standard for Binary Floating-Point Arithmetic; From -2ⁿ⁻¹ to 2ⁿ⁻¹-1 . You can use min_value() and max_value() to find min and max of each integer type, ex. i8::min_value();

  • u8 u16 u32 u64 : fixed size(bit) unsigned(+) integer types
DATA TYPE MIN MAX
u8 0 255
u16 0 65535
u32 0 4294967295
u64 0 18446744073709551615

💡 Same as signed numbers, min and max values are based on IEEE standard for Binary Floating-Point Arithmetic; From 0 to 2ⁿ-1 . Same way you can use min_value() and max_value() to find min and max of each integer type, ex. u8::max_value();

  • isize : variable sized signed(+/-) integer

Simply this is the data type to cover all signed integer types but memory allocates according to the size of a pointer. Min and max values are similar to i64 .

  • usize : variable sized unsigned(+) integer

Simply this is the data type to cover all unsigned integer types but memory allocates according to the size of a pointer. Min and max values are similar to u64.

  • f32 : 32-bit floating point

Similar to float in other languages, Single precision.

💡 Should avoid using this unless you need to reduce memory consumption badly or if you are doing low-level optimization, when targeted hardware not supports for double-precision or when single-precision is faster than double-precision on it.

  • f64 : 64-bit floating point

Similar to double in other languages, Double precision.

  • arrays : fixed-size list of elements of same data type
let a = [1, 2, 3]; // a[0] = 1, a[1] = 2, a[2] = 3
let mut b = [1, 2, 3];

let c: [int; 3] = [1, 2, 3]; //[Type; NO of elements]

let d: ["my value"; 3]; //["my value", "my value", "my value"];

let e: [i32; 0] = []; //empty array

println!("{:?}", a); //[1, 2, 3]
println!("{:#?}", a);
//  [
//      1,
//      2,
//      3
//  ]

⭐️ Arrays are immutable by default and also even with mut, its element count can not be changed.

🔎 If you are looking for a dynamic/growable array, you can use Vec. Vectors can contain any type of elements but all elements must be in the same data type.

  • tuples : fixed-size ordered list of elements of different(or same) data types
let a = (1, 1.5, true, 'a', "Hello, world!");
// a.0 = 1, a.1 = 1.5, a.2 = true, a.3 = 'a', a.4 = "Hello, world!"

let b: (i32, f64) = (1, 1.5);

let (c, d) = b; // c = 1, d = 1.5
let (e, _, _, _, f) = a; //e = 1, f = "Hello, world!", _ indicates not interested of that item

let g = (0,); //single-element tuple

let h = (b, (2, 4), 5); //((1, 1.5), (2, 4), 5)

println!("{:?}", a); //(1, 1.5, true, 'a', "Hello, world!")

⭐️ Tuples are also immutable by default and even with mut, its element count can not be changed. Also if you want to change an element’s value, new value should have the same data type of previous value.

  • slice : dynamically-sized reference to another data structure

Think you want to get/pass a part of an array or any other data structure. Instead of copy it to another array (or same data structure), Rust allows to create a view/reference to access only that part of data. And it can be mutable or not.

let a: [i32; 4] = [1, 2, 3, 4];//Parent Array

let b: &[i32] = &a; //Slicing whole array
let c = &a[0..4]; // From 0th position to 4th(excluding)
let d = &a[..]; //Slicing whole array

let e = &a[1..3]; //[2, 3]
let e = &a[1..]; //[2, 3, 4]
let e = &a[..3]; //[1, 2, 3]
  • str : unsized UTF-8 sequence of Unicode string slices
let a = "Hello, world."; //a: &'static str
let b: &str = "こんにちは, 世界!";

⭐️ It's an immutable/statically allocated slice holding an unknown sized sequence of UTF-8 code points stored in somewhere in memory. &str is used to borrow and assign the whole array to the given variable binding.

🔎 A String is a heap-allocated string. This string is growable, and is also guaranteed to be UTF-8. They are commonly created by converting from a string slice using the to_string() or String::from() methods. ex: “Hello”.to_string(); String::from("Hello");

💡 In general, you should use String when you need ownership, and &str when you just need to borrow a string.

  • functions

As we discussed on functions section, b is a function pointer, to plus_one function

fn plus_one(a: i32) -> i32 {
    a + 1
}

let b: fn(i32) -> i32 = plus_one;
let c = b(5); //6