Adding conditional logic with match guards

Originally published on php2rust.dev — part of the PHP to Rust course. View this lesson on the original site.

Match guards are if conditions after a pattern. The arm runs only when the pattern matches and the guard is true. PHP match has no guards; use if/else or conditions inside the arm.

Rust

struct Point { x: i32, y: i32 }

fn main() {
    let point = Point { x: 0, y: 10 };
    match point {
        Point { x: 0, y } if y < 5 => println!("On y-axis, close to origin"),
        Point { x: 0, y } => println!("On y-axis at {}", y),
        Point { x, y: 0 } if x > 5 => println!("On x-axis, far from origin"),
        Point { x, y } => println!("Point at ({}, {})", x, y),
    }
}

PHP

<?php
$point = ['x' => 0, 'y' => 10];
if ($point['x'] === 0 && $point['y'] < 5) {
    echo "On y-axis, close to origin\n";
} elseif ($point['x'] === 0) {
    echo "On y-axis at {$point['y']}\n";
} elseif ($point['y'] === 0 && $point['x'] > 5) {
    echo "On x-axis, far from origin\n";
} else {
    echo "Point at ({$point['x']}, {$point['y']})\n";
}

Comparison

• Rust: Guard is if condition after the pattern; combines pattern and extra checks.
• PHP: Logic expressed in if/elseif chains.
• Rust: Guards can refer to bindings from the pattern.
• PHP: No pattern syntax; use plain conditionals.

References

• Rust: Match guards
• PHP: if

What's next

Next: Matching ranges.

From PHP to Rust — Rust Syntax and Functions