Rust Essentials - Second Edition

Implementing the Drop trait

The following code snippet in which the Drop trait is implemented for a struct clearly shows the moment when the value block is freed:

// see code in Chapter 7/code/drop.rs 
struct Block { 
    number: i32 
} 
 
impl Drop for Block { 
    fn drop(&mut self) { 
        println!("Dropping!"); 
    } 
} 
 
fn print_block(block: Block) { 
    println!("In function print_block"); 
} 
 
fn main() { 
    let block = Block{ number: 1 }; 
    // move of value block: 
    print_block(block); 
    println!("Back in main!"); 
}

This prints out the following output:

In function print_blockDropping!Back in main!

So the block reference is freed at the end of the print_block function.