Add Complex Numbers exercise #528
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| "uuid": "ed6b5073-e3b1-4787-8551-ffffa9e7313d", | ||
| "practices": [], | ||
| "prerequisites": [], | ||
| "difficulty": 6 |
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The core of the exercise isn't that difficult, but relying heavily on operator overloading makes this more challenging
| local Complex | ||
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| Complex = function(r, i) | ||
| local c = { | ||
| -- | ||
| } | ||
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| return setmetatable(c, { | ||
| -- | ||
| }) | ||
| end | ||
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| return Complex |
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I tried to include a few breadcrumbs here to help lead people in the right direction
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You could add a document (maybe instructions.append.md) that links to the "Closure based objects" part of https://web.archive.org/web/20240104094707/http://lua-users.org/wiki/ObjectOrientationTutorial
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Sorry about the delay. I should be able to do this over the weekend.
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Thanks for the suggestion. I added an append to introduce closure-based OO and operator overloading.
| describe('operations between real numbers and complex numbers', function() | ||
| it('add real number to complex number', function() | ||
| assert.equal(Complex(6, 2), Complex(1, 2) + Complex(5)) | ||
| end) | ||
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| it('add complex number to real number', function() | ||
| assert.equal(Complex(6, 2), Complex(5) + Complex(1, 2)) | ||
| end) | ||
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| it('subtract real number from complex number', function() | ||
| assert.equal(Complex(1, 7), Complex(5, 7) - Complex(4)) | ||
| end) | ||
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| it('subtract complex number from real number', function() | ||
| assert.equal(Complex(-1, -7), Complex(4) - Complex(5, 7)) | ||
| end) | ||
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| it('multiply complex number by real number', function() | ||
| assert.equal(Complex(10, 25), Complex(2, 5) * Complex(5)) | ||
| end) | ||
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| it('multiply real number by complex number', function() | ||
| assert.equal(Complex(10, 25), Complex(5) * Complex(2, 5)) | ||
| end) | ||
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| it('divide complex number by real number', function() | ||
| assert.equal(Complex(1, 10), Complex(10, 100) / Complex(10)) | ||
| end) | ||
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| it('divide real number by complex number', function() | ||
| assert.equal(Complex(2.5, -2.5), Complex(5) / Complex(1, 1)) | ||
| end) | ||
| end) |
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Because I chose to use operator overloading this is a little bit awkward. I think it's worth it to introduce operator overloading.
| local Complex | ||
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| Complex = function(r, i) | ||
| local c = { | ||
| -- | ||
| } | ||
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| return setmetatable(c, { | ||
| -- | ||
| }) | ||
| end | ||
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| return Complex |
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You could add a document (maybe instructions.append.md) that links to the "Closure based objects" part of https://web.archive.org/web/20240104094707/http://lua-users.org/wiki/ObjectOrientationTutorial
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| it('imaginary unit', function() | ||
| assert.equal(Complex(-1, 0), Complex(0, 1) * Complex(0, 1)) | ||
| end) |
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I get a failure for this:
Failure → ./complex-numbers_spec.lua @ 36
complex-numbers imaginary unit
./complex-numbers_spec.lua:37: Expected objects to be equal.
Passed in:
(table: 0x563a518471c0) {
[i] = 0
[r] = -1 }
Expected:
(table: 0x563a51846650) {
[i] = 0
[r] = -1 }
Should the spec be assert.are.same because it appears to be checking whether it's actually the same table, rather than whether the table's properties are the same?
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The reason it uses assert.equal is because it expects your implementation to define equality via the __eq metamethod. This lets you define what equality means for your complex type without the tests requiring an identical internal representation for two complex numbers to be considered equal. This also gives you an opportunity to compare floating point values safely (see https://www.reddit.com/r/learnprogramming/comments/9y9gxs/small_lesson_of_the_day_never_check_two_floats/).
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The reason it uses
assert.equalis because it expects your implementation to define equality via the__eqmetamethod.
Got it. Thanks for the quick response!
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