rust basic -- types and ownership

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2023-01-12

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Types

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This is a summary of rust basic knowledge I learned from (Rust the Book)[https://doc.rust-lang.org/book/] chapter 1 ~ chapter 13 -I will use C to compare with since I familiar it.
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There are a bunch of built-in types we can work with: scalar types and compound types. -Those scalar types are just alike as C language.

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scalar types	rust	c
integer	i(u)8/i16/i32(default)/i64	(unsigned) char/short/int/long
float	f32/f64(default)	float/double
boolean	true/false	True/False (non-zero/zero)
character	char	char

The compound types are a bit different. rust provides many hands-on types where C type is not the same or needs to define explicitly.

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compound type	rust	c
struct	same	same
enum	enum element can be seen as key that could take value	represent numberic value, default starting from 0
array	vector	array
string	a wraper of vector	pointer of char *
tuple	exist	no such type in C

Variable declaration in rust is kinda tricky.

A normal declare syntax would be like let unmutable_variable = 3. This will imply that variable is i32 type -since the value we assign to is a integer and the default type for integer on most OS is i32. -We can explicit type by using type annotation: let unmutable_variable: u8 = 3. This will make variable -unmutable_variable is u8 type and has 3 as its value. We need to assign a value -to variable if we don't annotate type while declaration, otherwise compiler would prompt error.

Notice that, declaration as above one won't allow us to change value, if we want to be able to change variable's -value at runtime, we need to explicit it, for security reason:

let mut mutable_variable = 3;
-println!("first define: {mutable_variable}");
-mutable_variable = 5;
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-println!("change value to: {mutable_variable}");
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println!() is called macro, which would not cover for now.
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