We can specify that we want multiple expressions in the left-hand side pattern of the macro definition by adding a * for zero or more matches or a + for one or more matches. Let's see how we can do that with a simplified my_vec![] macro:
macro_rules! my_vec { ($($x: expr),*) => {{ let mut vector = Vec::new(); $(vector.push($x);)* vector }}}
Let's see what is happening here. First, we see that on the left side, we have two variables, denoted by the two $ signs. The first makes reference to the actual repetition. Each comma-separated expression will generate a $x variable. Then, on the right side, we use the various repetitions to push $x to the vector once for every expression we receive.
There is another new thing on the right-hand ...
