Match enum struct field with variable instead of literal [duplicate] - rust

Question

This question already has answers here:
How do I match based on a dynamic variable?
(4 answers)
Closed 6 months ago.
I am trying to match an enum struct. This enum has different variants with different (or none) fields, such as:
enum Enum {
One {n : usize},
Two ,
}
The match block that I am trying to achieve looks like:
match m {
Enum::One{n: special_value} => {
println!("it is special! {}", special);
}
Enum::One{n} => {
println!("not special: {}", n);
}
Enum::Two => {
println!("not special");
}
}
If I define let m = Enum::One{n: 3} and let special_value = 8 the code prints it is special! 3. This should print not special: 3.
If I change the match block to (note that I changed the variable special_value variable to the literal 8:
match m {
Enum::One { n: 8 } => {
println!("it is special!");
}
Enum::One { n } => {
println!("not special: {}", n);
}
Enum::Two => {
println!("not special");
}
}
Now defining let m = Enum::One { n: 3 } it prints as desired not special: 3.
In my actual project case, I cannot use a literal to do the match the value comes from the function call as a variable.
For this porpouse I can use this match block (note the special case has been removed and replaced by an if clause inside the general case) :
match m {
Enum::One { n } => {
if n == special_value {
println!("it is special! {}", special_value);
} else {
println!("not special: {}", n);
}
}
Enum::Two => {
println!("not special");
}
}
Is it possible to use a variable inside the match, or am I forced to use the if clause? What is the reason?

Answer 1

yes. you can add if statements on the match arm without creating if block inside match arm block
does this works for you?
enum Enum {
One {
n: usize
},
Two
}
fn main() {
let special_value = 123;
let m = Enum::One { n: 123 };
match m {
Enum::One { n } if n == special_value => println!("it is special! {}", special_value),
Enum::One { n } => println!("not special: {}", n),
Enum::Two => {
println!("not special");
}
}
}
https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=acfaae3976e7ca9fcf096c635a4daf98
works for me.