Keep a rational allocation amount exact

[SashaMIT]

Summary

• Money::Allocation.generate(Rational(1, 3), 1, false) returned 0.3333333333333333. The rational was converted through a float, so one part was not the original amount.
• A rational is now converted with to_d. One part of 1/3 matches Rational(1, 3).to_d.

Test plan

• Red: the allocation spec expected the to_d value and got the float approximation
• Green: rspec spec/money/allocation_spec.rb (23 examples, 0 failures)

Made with Cursor

[sunny]

Thank you. Can you add an entry to the CHANGELOG as well please?

[yukideluxe]

Thanks for fixing this! Just one comment (apart from adding the CHANGELOG line that @sunny requested) so we can wrap this up nicely 👍🏻

[yukideluxe]

Money has this customizable option

money/lib/money/money.rb

Lines 139 to 142 in 7348778

	# @!attribute [rw] conversion_precision
	# Used to specify precision for converting Rational to BigDecimal
	#
	# @return [Integer]

that is set to 16 by default but it's not used in this conversion 🙏🏻 Could we do number.to_d((Money.conversion_precision). According to Claude there are more places that it might not be respected but I need to look into this a bit more and it's totally unrelated to this PR anyways 😊

The tests will have to be tweaked too 🙏🏻

[SashaMIT]

Thanks, both notes are in. The changelog line is under Unreleased, and a Rational now goes through to_d(Money.conversion_precision). The spec expects that same precision. Rational(1, 3) at the default 16 is 0.3333333333333333.

[yukideluxe]

just a tweak in the spec!

[yukideluxe]

this test is running the code it tests and it currently passes in main so it's not actually testing the changes. Claudito suggests the following assertions and those look good to me!

it "converts a rational with Money.conversion_precision instead of through a float" do
  expect(described_class.generate(Rational(2, 3), 1, false)).to eq([BigDecimal("0.6666666666666667")])
  expect(described_class.generate(Rational(10**400, 1), 1, false)).to eq([BigDecimal("1e400")])
  expect(described_class.generate(Rational(1, 10**400), 1, false)).to eq([BigDecimal("1e-400")])
end

[sunny]

Claudito 😁

[SashaMIT]

Updated the spec to those three values. Rational(2, 3) is 0.6666666666666667, 10400 stays 1e400, and 1/10400 stays 1e-400. The conversion still goes through Money.conversion_precision.