Rust: Decision Making

Status: Courses Tags: Rust

if-else construct

1. if-else in Rust is not a statement but an expression.

   1. Statements do not return any value
   2. Expressions return value.

2. Hence if else in Rust return value which can be ignored or assigned to a variable

3. Both if and else branches should return the same type of value. Because Rust does not allow multiple types to be stored in a variable.

4. For example:

   #![allow(unused)]
   fn main() {
   // Simple example 
   if i < 10 {
      // the statement with semicolon hence the return value is ()
   	println!("Value is less than 10");
   } else {
      println!("Value is more than 10");
   }
   
   // complex example
   let result = if i < 10 {
      // the statement without semicolon is considered as return value
      1
   } else {
      // 0 is returned, and type is kept same
      0
   }
   }

   match expression

   1. match in Rust is a replacement to switch and case in C.

   2. For Example:

      // Simple match usage
      
      // Returns an HTTP status
      fn req_status() -> u32 {
      	200
      }
      
      fn main() {
      	let status = req_status();
      	let result = match status {
      		200 => {
      			println!("HTTP Success!");	
      		},
      		404 => println!("Page not found!"),
          other => println!("Reequest Failed, Status code {}!", other);
      	}
      }

   3. match statement has to have branches for all the possible cases (match exhaustively). i.e in the Above case, we have to match against all the numbers until a maximum of u32.

   4. other is used to catch all and store the value.

   5. _ is used to catch all and ignore the value.

   6. match is an expression so it returns a value.

   7. Each branch in match should return the same type of value because Rust does not allow one variable to store multiple types.