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Merge pull request #101 from peter-gribanov/lsp3

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Liskov Substitution Principle (LSP)
This commit is contained in:
Tomáš Votruba
2018-02-26 22:27:25 +01:00
committed by GitHub
parent a1ac1b0804 6c1da67e28
commit b19b3a1fd2
1 changed files with 34 additions and 42 deletions
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README.md
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@@ -1677,11 +1677,6 @@ class Rectangle
protected $width = 0; protected $width = 0;
protected $height = 0; protected $height = 0;
public function render(int $area): void
{
// ...
}
public function setWidth(int $width): void public function setWidth(int $width): void
{ {
$this->width = $width; $this->width = $width;
@@ -1711,40 +1706,40 @@ class Square extends Rectangle
} }
} }
/** function printArea(Rectangle $rectangle): void
* @param Rectangle[] $rectangles
*/
function renderLargeRectangles(array $rectangles): void
{ {
foreach ($rectangles as $rectangle) { $rectangle->setWidth(4);
$rectangle->setWidth(4); $rectangle->setHeight(5);
$rectangle->setHeight(5);
$area = $rectangle->getArea(); // BAD: Will return 25 for Square. Should be 20. // BAD: Will return 25 for Square. Should be 20.
$rectangle->render($area); echo sprintf('%s has area %d.', get_class($rectangle), $rectangle->getArea()).PHP_EOL;
}
} }
$rectangles = [new Rectangle(), new Rectangle(), new Square()]; $rectangles = [new Rectangle(), new Square()];
renderLargeRectangles($rectangles);
foreach ($rectangles as $rectangle) {
printArea($rectangle);
}
``` ```
**Good:** **Good:**
```php The best way is separate the quadrangles and allocation of a more general subtype for both shapes.
abstract class Shape
{
abstract public function getArea(): int;
public function render(int $area): void Despite the apparent similarity of the square and the rectangle, they are different.
{ A square has much in common with a rhombus, and a rectangle with a parallelogram, but they are not subtype.
// ... A square, a rectangle, a rhombus and a parallelogram are separate shapes with their own properties, albeit similar.
}
```php
interface Shape
{
public function getArea(): int;
} }
class Rectangle extends Shape class Rectangle implements Shape
{ {
private $width; private $width = 0;
private $height; private $height = 0;
public function __construct(int $width, int $height) public function __construct(int $width, int $height)
{ {
@@ -1758,9 +1753,9 @@ class Rectangle extends Shape
} }
} }
class Square extends Shape class Square implements Shape
{ {
private $length; private $length = 0;
public function __construct(int $length) public function __construct(int $length)
{ {
@@ -1769,23 +1764,20 @@ class Square extends Shape
public function getArea(): int public function getArea(): int
{ {
return pow($this->length, 2);        return $this->length ** 2;
}    }
} }
/** function printArea(Shape $shape): void
* @param Rectangle[] $rectangles
*/
function renderLargeRectangles(array $rectangles): void
{ {
foreach ($rectangles as $rectangle) { echo sprintf('%s has area %d.', get_class($shape), $shape->getArea()).PHP_EOL;
$area = $rectangle->getArea();
$rectangle->render($area);
}
} }
$shapes = [new Rectangle(4, 5), new Rectangle(4, 5), new Square(5)]; $shapes = [new Rectangle(4, 5), new Square(5)];
renderLargeRectangles($shapes);
foreach ($shapes as $shape) {
printArea($shape);
}
``` ```
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