Do all primitive types implement the Copy trait?

Question

Do all primitive types in Rust implement the Copy trait?

It would be interesting to know, as surely such knowledge is part of a thorough learning of a new programming language.

Answer 1

We can use the compiler to prove if something implements Copy. Using the list of primitives from The Rust Programming Language:

fn is_copy<T: Copy>() {}

fn main() {
    is_copy::<bool>();
    is_copy::<char>();
    is_copy::<i8>();
    is_copy::<i16>();
    is_copy::<i32>();
    is_copy::<i64>();
    is_copy::<u8>();
    is_copy::<u16>();
    is_copy::<u32>();
    is_copy::<u64>();
    is_copy::<isize>();
    is_copy::<usize>();
    is_copy::<f32>();
    is_copy::<f64>();
    is_copy::<fn()>();
}

There are a few other types I'd consider "primitive":

• Immutable references (&T)
• Mutable references (&mut T)
• Raw pointers (*const T / *mut T)

Immutable references always implement Copy, mutable references never implement Copy, and raw pointers always implement Copy:

// OK
is_copy::<&String>();
is_copy::<*const String>();
is_copy::<*mut String>();
// Not OK
is_copy::<&mut i32>();

There are a few other types from the book's list:

• Tuples
• Arrays

These types can contain many types; they are parameterized over a generic. They are only Copy if all the contained values are Copy:

// OK
is_copy::<[i32; 1]>();
is_copy::<(i32, i32)>();
// Not OK
is_copy::<[Vec<i32>; 1]>();
is_copy::<(Vec<i32>, Vec<i32>)>();

• Slices

Slices are doubly special. The slice type itself ([T]) and string slices (str) are unsized types. It's very rare to see them without an indirection of some kind, often a reference (&[T] / &str). The unsized values cannot exist by themselves. The version behind a reference behaves like references do.

// OK
is_copy::<&str>();
is_copy::<&[i32]>();
// Not OK
is_copy::<str>();
is_copy::<[i32]>();

And as always, the documentation for a trait lists everything that implements that trait. (Except when there are bugs in the documentation).