episode-007

Where we discover types

Setup

The following needs to be prepared

• A project called types
• Some example code with a &str and a i32

Script

We used variables to bind values to names, as seen in this code.

let message = "Hello, world!";

println!("{}", message);

let answer = 42;

println!("the answer is {}", answer);

But the declaration of the variables is not complete. What is missing is the type declaration. For example answer has type i32.

let answer: i32 = 42;

The reason that Rust allows you to declare a variable without explicitly mentioning the type is type inference. Rust can often deduce the type of an expression, making an explicit declaration superfluous.

Sometimes we want to have more control over the type of a variable. The are numerous integer types like, for example i8, i16, i32 and i64, that differ in the amount of bits that is used to represent the value.

The type also influences the program. If we change the value of the answer to 255 and go down the mentioned types i64, i32, i16 until i8, we see that it overflows into -1. Notice that Rust warns us about that behavior.

And there you have it, we discovered types.