Create Vec<String> from literal - rust

Question

I want to do
fn main() {
let options: Vec<String> = vec!["a", "b", "c"].map(|s| s.to_owned()).collect();
}
because this seems like the easiest way to get a vector of owned Strings, but I get hit with this error:
error: no method named `map` found for type `std::vec::Vec<&str>` in the current scope
...
note: the method `map` exists but the following trait bounds were not satisfied:
`std::vec::Vec<&str> : std::iter::Iterator`, `[&str] : std::iter::Iterator`
I don't see where the need for the [&str] : std::iter::Iterator bound comes from. if you ignore the part with split_whitespace I'm basically doing what answers on this question recommend.
How should I be generating this vector?

Answer 1

if you ignore the part with split_whitespace
Yes, except you cannot ignore this part. The docs for split_whitespace state (emphasis mine):
The iterator returned
split_whitespace returns an iterator over the pieces of the string that were separated by whitespace, and map is a method on Iterator.
A Vec is not an iterator. You can see that Vec does not implement it's own map method:
no method named map found for type std::vec::Vec<&str>
And the compiler tries to suggest what you might have meant, but weren't quite achieving:
note: the method map exists but the following trait bounds were not satisfied:
You can get an iterator from a Vec by calling Vec::iter or into_iter:
fn main() {
let options: Vec<String> = vec!["a", "b", "c"].into_iter().map(|s| s.to_owned()).collect();
}
However, there's no need to allocate two vectors here, an array and a vector is more efficient:
let options: Vec<_> = ["a", "b", "c"].iter().map(|s| s.to_string()).collect();
An iterator over a slice returns references (&T) to the elements in the slice. Since each element is already a &str, the type of s is a &&str. Calling to_owned on a reference to a reference simply clones the reference. You could also have said .map(|&s| s.to_owned()), which dereferences the value once, producing a &str. Calling to_owned on a &str allocates a String.

Answer 2

If I had to create vectors of Strings repeatedly, I would use a macro:
macro_rules! vec_of_strings {
// match a list of expressions separated by comma:
($($str:expr),*) => ({
// create a Vec with this list of expressions,
// calling String::from on each:
vec![$(String::from($str),)*] as Vec<String>
});
}
fn main() {
let v1 = vec_of_strings![];
let v2 = vec_of_strings!["hello", "world", "!"];
println!("{:?}", v1);
println!("{:?}", v2);
}
Output:
[]
["hello", "world", "!"]