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What even is a JSON number?

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Re: What even is a JSON number?

#101

Post by lifthrasiir »

int_19h wrote: post #79
olejorgenb wrote: post #45

Earlier quoted context omitted.

Agreed, this can be a pain. Python by default serialize and de-serialize the `NaN` literal, making you pay some cleanup cost once you need to interopt with other systems. (same for `Inf`) Say what you want about NaN, but IEEE 754 is the facto way of dealing with floating points in computers and even if NaNs and Infs are a bit "fringe" it's unfortunate that the most popular serialization format can not represent these…

There are so many things that are poorly thought out or underspecified in JSON, it's amazing that it got so widely adopted for interop. No wonder that it became a perpetual source of serialization bugs.

Especially annoying given that they could have been easily adopted. Infinity could've been encoded as `1/0` (among most other possibilities). NaN could've been encoded as `0/0` (again, among most other possibilities). JSON doesn't allow all possible JavaScript literals anyway, so these encodings might have been worked if they were somehow standardized.

Re: What even is a JSON number?

#102

Post by esrauch »

beryilma wrote: post #49
01HNNWZ0MV43FF wrote: post #40

Earlier quoted context omitted.

Makes sense for dollars, but for anything like graphics or physics I'd consider a power of two like 1,024 as the fixed-point factor instead. My intuition tells me that "x * 1000 / 1000 == x" might not be true for all numbers if you're using floats.

A sure sign of an inexperienced programmer in numerical computing is when they check for equality to zero of a floating-point number as if (x == 0) ... instead of something like if (abs(x) where eps is a suitably defined small number.

I think funny enough a sure sign of an inexperienced programmer in bigco application programming is the other way around, that they wrongly learn a metal model of "floating point is approximate, never ever do ==" in school.

Re: What even is a JSON number?

#103

Post by incorrecthorse »

yawaramin wrote: post #76

Long story short: don't use JSON numbers to represent money or monetary rates. Always use decimals encoded as string. It's surprising how many APIs fall short of this basic bar.

No. Use integers to store the smallest money decimal, and store the currency name alongside.

Re: What even is a JSON number?

#104

Post by imtringued »

golergka wrote: post #66
greggyb wrote: post #65

Earlier quoted context omitted.

Until you want faster joins, in which case, comparisons of integers tend to be much faster on hardware I am aware of than string comparisons.

We're talking about deserialising JSONs in the application server here, nobody stops you from treating ids as numbers on the database side of things. But also, this sounds like a premature optimisation. Most applications will never reach a level where their performance is actually impacted by string comparison, and when you reach that stage, you're likely have already thrown out a lot of other common sense stuff like…

People use integer data types for primary keys in databases all the time. There is nothing wrong with it.

Re: What even is a JSON number?

#105

Post by billpg »

"ID numbers start from 2^53 and are allocated sequentially including odd numbers that are not compatible with "double" types. Please ensure you are reading this value as a 64-bit integer."

Re: What even is a JSON number?

#106

Post by sjducb »

incorrecthorse wrote: post #103
yawaramin wrote: post #76

Long story short: don't use JSON numbers to represent money or monetary rates. Always use decimals encoded as string. It's surprising how many APIs fall short of this basic bar.

No. Use integers to store the smallest money decimal, and store the currency name alongside.

What happens if you’re sure that four decimal places is the smallest, then suddenly a partner system starts sending you 6 decimal places?

Re: What even is a JSON number?

#108

Post by berkes »

whalesalad wrote: post #12

I tend to end up encoding everything as an integer (multiply by 1000, 10000 etc) and then turn it back into a float/decimal on decode. For instance if I am building a system dealing with dollar amounts I will store cent amounts everywhere, communicate cent amounts over the wire, etc. then treat it as a presentation concern to render it as a dollar amount.

For money, that's a sane setup.

But do note, that in currency, there are multiple, actively used currencies that have zero, three, five (rare) or even eight (BTC) decimals. That some decimals cannot be divided by all numbers (e.g. only 0.5)

Point being: floats are dangerously naive for currency. But integers are naive too. You'll most probably want a "currency" or "money" type. Some Value Object, or even Domain Model.

XML offered all this, but in JSON there's little to convey this, other than some nested "object" with at least the decimal amt (as int), and the ISO4217 currency. And maybe -depending on how HATEOAS you wanna be- a formatting string to be used in locales, a rule on divisibility and/or how many decimal places your int or decimal might be.

(FWIW, I built backbends for financial systems and apps. It gets worse than this if you do math on the currencies. Some legislatioins or bookkeeping rules state that calculation uses more or less decimals. E.g. that ($10/3)*3 == $10 vs == $9.99. or that $0.03/2 == 0.1 + 0.2, e.g. when splitting a bill. This stuff is complex, but real domain logic)

Re: What even is a JSON number?

#109

Post by berkes »

berkes wrote: post #108
whalesalad wrote: post #12

I tend to end up encoding everything as an integer (multiply by 1000, 10000 etc) and then turn it back into a float/decimal on decode. For instance if I am building a system dealing with dollar amounts I will store cent amounts everywhere, communicate cent amounts over the wire, etc. then treat it as a presentation concern to render it as a dollar amount.

For money, that's a sane setup. But do note, that in currency, there are multiple, actively used currencies that have zero, three, five (rare) or even eight (BTC) decimals. That some decimals cannot be divided by all numbers (e.g. only 0.5) Point being: floats are dangerously naive for currency. But integers are naive too. You'll most probably want a "currency" or "money" type. Some Value Object, or even Domain Model…

When I say dangerously naive, I mean in a way that people can go to jail¹ for "loosing" or "inventing" cents. Which your software will do if you use floats.

¹IANAL. But this was told when legal people looked at our architecture.

Re: What even is a JSON number?

#110

Post by Macha »

sjducb wrote: post #106
incorrecthorse wrote: post #103

Earlier quoted context omitted.

No. Use integers to store the smallest money decimal, and store the currency name alongside.

What happens if you’re sure that four decimal places is the smallest, then suddenly a partner system starts sending you 6 decimal places?

Precision should be part of the spec for integrations. With the integer multiple of minimal unit, that makes it clear in the API what it is.

e.g. it doesn't make sense to support billing in sub-currency unit amounts just by allowing it in your API definition, as you're going to need to batch that until you get a billable amount which is larger than the fee for issuing a bill. Even for something like $100,000.1234, the bank doesn't let you do a transfer for 0.34c.

For cases where sub-currency unit billing is a thing, it should be agreed what the minimal unit is (e.g. advertising has largely standardised on millicents)

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