サンプル

Hold money in shopspring/decimal without losing cents to Div, ==, or String()

sha256:84206d243236399467879a1efbd7f91542f9c90b1d044a06e8611694204998bd

ケース

ゴール

Hold money in shopspring/decimal without losing cents to Div, ==, or String() HOW

パッケージ

github.com/shopspring/decimal 1.4.0

環境

go 1.26

作成日

2026-08-14T08:53:07Z

コントラクト

• assert NewFromFloat(0.1).String() is "0.1" and Equal to NewFromString("0.1"), so the constructor is not where 0.1 goes wrong
• assert the loss happens in float64 before the constructor, including digits float64 cannot hold at all
• assert Go folds untyped constant 0.1+0.2 exactly, so the demo only misbehaves once the operands are variables
• assert Add and Mul are exact where the float64 equivalents give 7.000000000000001 and 3.3000000000000003
• assert Mul adds the exponents of its operands while Add and Sub keep the finer of the two, and the Sum identity decimal.Zero is New(0,1) rather than New(0,0)
• assert DivisionPrecision defaults to 16 and is a mutable global, so (1/3)*3 is 0.9999999999999999 and not 1
• assert Div rounds rather than truncates, so 2/3 ends in a 7, and DivRound takes the precision as an argument
• assert QuoRem returns the exact remainder and splitting 10.00 three ways adds back up to 10.00, while a total finer than the split scale pays out a cent more
• assert Equal compares values while == compares the *big.Int pointer and the scale, so two parses of "1.0" are not ==
• assert the zero value is a usable 0 that is Equal to decimal.Zero but not == to New(0,0)
• assert Cmp orders numerically and drops into slices.SortFunc as a method expression
• assert Round is half away from zero and RoundBank is half to even, that they agree wherever the digit ahead of the half is odd, and that the disagreement moves a four-line invoice total by two cents
• assert rounding cents through float64 obeys neither rule, because 1.005 falls below the half and 8.045 lands exactly on it
• assert String() trims trailing zeros while the exponent stays -2, and StringFixed / StringFixedBank are the money formats
• assert NewFromString rejects "1,005" instead of guessing a number

ファイル

• csx.json
• go.mod
• go.sum
• src/money.go
• test/main.go

オリジンシーダー

anonymous

検証レシート

• go 1.26 · CONTAINER_RUN · compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS · golang@1 · 2026-08-14 · ed25519:a2ec939a4c60e243
• · CONTAINER_RUN · compile:SKIPPED · contract:FAIL · load:SKIPPED · resolve:PASS · golang@1 · 2026-08-14 · ed25519:7da3f610facce8bf