New upstream version 1.49.0+dfsg1

[rustc.git] / src / doc / rust-by-example / src / types / literals.md

# Literals

Numeric literals can be type annotated by adding the type as a suffix. As an example, 
to specify that the literal `42` should have the type `i32`, write `42i32`.

The type of unsuffixed numeric literals will depend on how they are used. If no
constraint exists, the compiler will use `i32` for integers, and `f64` for
floating-point numbers.

```rust,editable
fn main() {
    // Suffixed literals, their types are known at initialization
    let x = 1u8;
    let y = 2u32;
    let z = 3f32;

    // Unsuffixed literals, their types depend on how they are used
    let i = 1;
    let f = 1.0;

    // `size_of_val` returns the size of a variable in bytes
    println!("size of `x` in bytes: {}", std::mem::size_of_val(&x));
    println!("size of `y` in bytes: {}", std::mem::size_of_val(&y));
    println!("size of `z` in bytes: {}", std::mem::size_of_val(&z));
    println!("size of `i` in bytes: {}", std::mem::size_of_val(&i));
    println!("size of `f` in bytes: {}", std::mem::size_of_val(&f));
}
```

There are some concepts used in the previous code that haven't been explained
yet, here's a brief explanation for the impatient readers:

* `std::mem::size_of_val` is a function, but called with its *full path*. Code
  can be split in logical units called *modules*. In this case, the
  `size_of_val` function is defined in the `mem` module, and the `mem` module
  is defined in the `std` *crate*. For more details, see
  [modules][mod] and [crates][crate].

[mod]: ../mod.md
[crate]: ../crates.md