Kotlin Money
Languages and libraries
money library
SHOW HN2024
427points
228comments
#99of 3,515 in 2024
Top 3%of 2024 by points
How HN took it
CuriousMostly questions and neutral comments
8 positive, 43 neutral or asking, 1 mixed, 22 critical, out of 74 comments about the project. Thread score -0.14.
Design: 3 for, 15 againstIdea: 2 for, 7 againstExecution: 2 for, 0 against
The thread, comment by comment
Each row is a top-level comment and its replies, in HN's order. Select a cell to open that comment on HN.
positive neutral or mixed critical about another commenter or something else the maker
What HN said
What people liked
Useful API and good ergonomics compared to alternatives
From 2 comments
Nice library! Manipulating money is probably trickiest thing since time was invented. Library looks very usable. I have to ask though: > val transactionFee = 1.25.percent() //…
Ygg2 on HNNice. Looks like it satisfies all the requirements detailed here [0]. Also, good discussion of the major difficulty dealing with money here [1]. [0]…
donjigweed on HN
Allocation feature is useful for splitting amounts
From 1 comment
I just had to implement the 'allocate' functionality described here, specifically with the %-based weights, and it was a pain that required careful comments to ensure was clear!…
monkaiju on HN
Objections
Too much infix notation makes the API hard to read
From 3 comments
My only complaint is that there seems to be too much infix. Why not just do 50.btc, 25.3.usd This would keep it inline with the time API doing 20.seconds Also percentages could…
Exerosis on HNInfix functions is one of the worst features of Kotlin.
wiseowise on HNKotlin has the problem of "I had N problems, so I think I can create 1 new solution, now I have N+1 problems" (obligatory https://xkcd.com/927/). The 'money/percent/usd' are…
textlapse on HN
No support for cash rounding rules yet
From 1 comment
This is something I am aware but there is no support for this rounding scheme at the moment.
eriksencosta on HN
Prior art exists in Java Money, F# units of measure and other languages
From 3 comments
Java has JSR 354 for money [1]. There is also a reference implementation [2]. So there is official support for money in Java. [1] https://jcp.org/en/jsr/detail?id=354 [2]…
jsiepkes on HN> no mainstream language has a first-class data type for representing money I don't think that's correct, absent some no-true-scotsman gymnastics. F# has units-of-measure (UoM)…
psd1 on HNC# has a decimal type: "The decimal type is a 128-bit data type suitable for financial and monetary calculations."…
yett on HN
Requests
Cash rounding support
From 1 comment
Does this library handle rounding rules [0]? In many countries, prices are rounded to the nearest 5 cent, but the rules can often be elaborate. It looks like the allocation…
Etheryte on HN
Localization of currency symbols
From 1 comment
I like the support for custom currencies, as that is an edge case that often pops up. On the other hand, be careful about tying the symbol to the currency, as symbols are locale…
bojanz on HN
Compile-time currency mismatch checks
From 2 comments
Neat. It seems to me like this is filling three separate gaps: ``` - fixed point arithmetic - tagging values with units - localization for parsing currency names into units ```…
rebeccaskinner on HNI think most of this is covered by a good Decimal API, currency stuff probably shouldn't be embedded into a language because it changes: currencies come and go, get redenominated…
boronine on HN
Questions
How does adding different currencies behave
From 1 comment
I have questions about some edge cases I've encountered in dealing with money. - Let's say I load two money values from a database. Value A is 1 USD and value B is 1 BTC. If I…
hathawsh on HN
How is rounding configured
From 2 comments
I have questions about some edge cases I've encountered in dealing with money. - Let's say I load two money values from a database. Value A is 1 USD and value B is 1 BTC. If I…
hathawsh on HNThanks for the questions. Answers: 1. You get an exception 2. You may specify the rounding rule: https://github.com/eriksencosta/money/blob/trunk/docs/usage/rounding.md 3. It has…
eriksencosta on HN
Alternatives named
Java Money (JSR 354 / Moneta)
From 2 comments
Java has JSR 354 for money [1]. There is also a reference implementation [2]. So there is official support for money in Java. [1] https://jcp.org/en/jsr/detail?id=354 [2]…
jsiepkes on HNHow does it compare to the Java money API (https://jcp.org/en/jsr/detail?id=354) and the related Kotlin DSL in…
hiddew on HN
F# units of measure
From 1 comment
> no mainstream language has a first-class data type for representing money I don't think that's correct, absent some no-true-scotsman gymnastics. F# has units-of-measure (UoM)…
psd1 on HN
C# and Delphi decimal/currency types
From 2 comments
C# has a decimal type: "The decimal type is a 128-bit data type suitable for financial and monetary calculations."…
yett on HNDelphi has a currency type, as does C++Builder (so, a native Currency type available in C++ with that toolchain.) This one seems to carry units, as in, it is not a type with math…
vintagedave on HN