How do I print the type of a variable in Rust?

Question

I have the following:

let mut my_number = 32.90;

How do I print the type of my_number?

Using type and

Answer 1

Some other answers don't work, but I find that the typename crate works.

1. Create a new project:

   cargo new test_typename
   

2. Modify the Cargo.toml

   [dependencies]
   typename = "0.1.1"
   

3. Modify your source code

   use typename::TypeName;
   
   fn main() {
       assert_eq!(String::type_name(), "std::string::String");
       assert_eq!(Vec::::type_name(), "std::vec::Vec");
       assert_eq!([0, 1, 2].type_name_of(), "[i32; 3]");
   
       let a = 65u8;
       let b = b'A';
       let c = 65;
       let d = 65i8;
       let e = 65i32;
       let f = 65u32;
   
       let arr = [1,2,3,4,5];
       let first = arr[0];
   
       println!("type of a 65u8  {} is {}", a, a.type_name_of());
       println!("type of b b'A'  {} is {}", b, b.type_name_of());
       println!("type of c 65    {} is {}", c, c.type_name_of());
       println!("type of d 65i8  {} is {}", d, d.type_name_of());
       println!("type of e 65i32 {} is {}", e, e.type_name_of());
       println!("type of f 65u32 {} is {}", f, f.type_name_of());
   
       println!("type of arr {:?} is {}", arr, arr.type_name_of());
       println!("type of first {} is {}", first, first.type_name_of());
   }
   

The output is:

type of a 65u8  65 is u8
type of b b'A'  65 is u8
type of c 65    65 is i32
type of d 65i8  65 is i8
type of e 65i32 65 is i32
type of f 65u32 65 is u32
type of arr [1, 2, 3, 4, 5] is [i32; 5]
type of first 1 is i32