Rust
Struct patterns
Destructure struct fields with patterns.
Struct patterns
Patterns can both unpack struct fields and match them against specific values. Fields with literal values act as filters, named fields bind; .. ignores the rest:
struct Nokta { x: i32, y: i32 }
fn konum(p: &Nokta) -> String {
match p {
Nokta { x: 0, y } => format!("y ekseninde {y}"),
Nokta { x, y: 0 } => format!("x ekseninde {x}"),
Nokta { x, y } => format!("düzlemde ({x}, {y})"),
}
}
If the field name and variable name match, the shorthand is used; for a different name write Nokta { x: yatay, .. }.
Matching through a reference
In match p, p is a &Nokta but the patterns are written as Nokta { .. }. Thanks to "match ergonomics", the compiler adapts the pattern to the reference automatically, and the bound x, y variables become &i32. Comparing with literals (x: 0) still works.
let noktalar = [Nokta { x: 0, y: 3 }, Nokta { x: 2, y: 0 }];
for p in &noktalar {
println!("{}", konum(p));
}
Exercise Classify positions
Write the Nokta struct above and the konum function. Print the results for the points (0, 3), (2, 0) and (1, 1) on separate lines.
Show example solution
struct Nokta {
x: i32,
y: i32,
}
fn konum(p: &Nokta) -> String {
match p {
Nokta { x: 0, y } => format!("y ekseninde {y}"),
Nokta { x, y: 0 } => format!("x ekseninde {x}"),
Nokta { x, y } => format!("düzlemde ({x}, {y})"),
}
}
fn main() {
let noktalar = [Nokta { x: 0, y: 3 }, Nokta { x: 2, y: 0 }, Nokta { x: 1, y: 1 }];
for p in &noktalar {
println!("{}", konum(p));
}
}
Test yourself
-
Which arm does <code>Nokta { x: 0, y: 0 }</code> take in the match above?
- The second arm
- The third arm
- None
- The first arm: "y ekseninde 0"
Show answer
The first arm: "y ekseninde 0" — Arms are tried in order; x: 0 satisfies the first arm, so it stops there. If you want a separate arm for the origin, write it at the top.
-
Match a literal, bind the rest
match p {
Nokta { x: ____, y } => format!("y ekseninde {y}"),
_ => String::new(),
}
Show answer
match p {
Nokta { x: 0, y } => format!("y ekseninde {y}"),
_ => String::new(),
}
-
Point and result
- Nokta { x: 0, y: 3 }
- y ekseninde 3
- Nokta { x: 2, y: 0 }
- x ekseninde 2
- Nokta { x: 1, y: 1 }
- düzlemde (1, 1)
- Nokta { x: 0, y: 0 }
- y ekseninde 0
Next lesson: Destructuring
