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Inverting FactorUnitPart calculates the reciprocal of its ratio #28

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Inverting FactorUnitPart calculates the reciprocal of its ratio #28

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8 changes: 8 additions & 0 deletions src/FactorUnitPart.php
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Original file line number Diff line number Diff line change
Expand Up @@ -14,4 +14,12 @@ public function format(): string
{
return "{$this->getRatio()}";
}

#[\Override]
public function invert(): self
{
// A FactorUnitPart always has power = 1. So when inverting it,
// we calculate the reciprocal of the ratio instead of negating the power.
return new self(1 / $this->getRatio());
}
}
12 changes: 12 additions & 0 deletions tests/FactorUnitPartTest.php
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Expand Up @@ -18,4 +18,16 @@ public function test_stringifies()
{
$this->assertEquals('100', (string)new FactorUnitPart(100));
}

public function test_inverts()
{
$factor = new FactorUnitPart(100);

$factorInverted = $factor->invert();

$this->assertEquals(FactorUnitPart::class, get_class($factorInverted));
$this->assertNull($factorInverted->getDimension());
$this->assertEquals(0.01, $factorInverted->getRatio());
$this->assertEquals(1, $factorInverted->getPower());
}
}
46 changes: 46 additions & 0 deletions tests/UnitTest.php
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Expand Up @@ -171,4 +171,50 @@ public function test_divide()

$this->assertEquals($ms->getDimensions(), $meterDividedBySeconds->getDimensions());
}

public function test_invert()
{
$hundredSquareMeters = new Unit(
new FactorUnitPart(100),
new UnitPart(1, Dimension::LENGTH, 2),
);

$inverted = $hundredSquareMeters->invert();

$this->assertEquals(-2, $inverted->getDimensions()[Dimension::LENGTH->name]);
$this->assertEquals(0.01, $inverted->getRatio());
}

public function test_invert_twice()
{
$hundredSquareMeters = new Unit(
new FactorUnitPart(100),
new UnitPart(1, Dimension::LENGTH, 2),
);

$invertedTwice = $hundredSquareMeters->invert()->invert();

$this->assertEquals($invertedTwice->getRatio(), $hundredSquareMeters->getRatio());
$this->assertEquals($invertedTwice->getDimensions(), $hundredSquareMeters->getDimensions());
Comment on lines +197 to +198
}

public function test_unit_and_factor_mix()
{
// 100m^2
$hundredSquareMeters = new Unit(
new FactorUnitPart(100),
new UnitPart(1, Dimension::LENGTH, 2),
);

// (10m)^2
$tenMetersSquared = new Unit(
new UnitPart(10, Dimension::LENGTH, 2),
);

$this->assertEquals($hundredSquareMeters->getRatio(), $tenMetersSquared->getRatio());
$this->assertEquals($hundredSquareMeters->getDimensions(), $tenMetersSquared->getDimensions());

$this->assertEquals($hundredSquareMeters->invert()->getRatio(), $tenMetersSquared->invert()->getRatio());
$this->assertEquals($hundredSquareMeters->invert()->getDimensions(), $tenMetersSquared->invert()->getDimensions());
}
}
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