At the lowest level, no, you can't read enum fields without a match
1.
Methods on an enum can provide more convenient access to data within the enum (e.g. Result::unwrap
), but under the hood, they're always implemented with a match
.
If you know that a particular case in a match
is unreachable, a common practice is to write unreachable!()
on that branch (unreachable!()
simply expands to a panic!()
with a specific message).
1 If you have an enum with only one variant, you could also write a simple let
statement to deconstruct the enum. Patterns in let
and match
statements must be exhaustive, and pattern matching the single variant from an enum is exhaustive. But enums with only one variant are pretty much never used; a struct would do the job just fine. And if you intend to add variants later, you're better off writing a match
right away.
enum Single {
S(i32),
}
fn main() {
let a = Single::S(1);
let Single::S(b) = a;
println!("{}", b);
}
On the other hand, if you have an enum with more than one variant, you can also use if let
and while let
if you're interested in the data from a single variant only. While let
and match
require exhaustive patterns, if let
and while let
accept non-exhaustive patterns. You'll often see them used with Option
:
fn main() {
if let Some(x) = std::env::args().len().checked_add(1) {
println!("{}", x);
} else {
println!("too many args :(");
}
}
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