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Null Island

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How does one keep a bouy moored in 5km deep water?

It’s moored with a 16,210 foot cable. It is a weather station as well.

https://www.ndbc.noaa.gov/station_page.php?station=13010

The mooring itself allows for some sway due to current.

https://en.m.wikipedia.org/wiki/Mooring_(oceanography)

From https://en.wikipedia.org/wiki/Weather_buoy (linked from the Null Island article):

> Moored buoys are connected with the ocean bottom using either chains, nylon, or buoyant polypropylene.

5.1km cables.

That would allow for quite a bit of drift–a kilometer in each direction.

In practice, it's often more. A swing radius of several nautical miles is fairly normal.

My knowledge is rusty, but, IIRC, for a shallow water mooring buoy you assume a radius of about half the water's depth. I'm not sure if there's a similar rule of thumb for deep water buoys.

Three of them, set in different directions.

I’m not saying that’s definitely how it’s done, but it’s how I’d think to do it with nothing other than my naïve geometric education.

Sounds quite expensive. Not sure if the exact position of the buoy is considered that important.

How?

Pythagorean Theorem: distance = sqrt(5.1^2 + 5^2) ≈ 1.005km.

With the actual depth, 4.94km, not 5km, 5.1 km would give distance = sqrt(5.1^2 + 4.94^2) ≈ 1.267km.

I guess you meant -, not +. Indeed, though I know the relevant formula, my intuition so violently failed me that I didn’t even calculate it before deciding it couldn’t be so large.

Doh, yes!

https://www.wired.com/2015/11/null/

In Smalltalk it is called nil. nil is an instance of the class UndefinedObject. In principle you could subclass UndefinedObject. But what is interesting is that you can add more instance methods to the class UndefinedObject so you could define the method #isNil for instance which could be defined also for all objects, but differently

In JavaScript there's a distinction between 'null' and 'undefined'.

You can pick your own semantics for them but I think 'undefined' more or less means "not known" while null means "known not to exist".

Agreed, but just wanted to add the context that you get undefined values by trying to access uninitialised things such as out of bounds array elements, get on a map-like object with a key that's yet to be set, unset properties on a object, return value of a function that returns void, etc.

In Ruby, nil is a singleton instance of NilClass, and defines #nil?, as well as methods to cast to different types e.g. nil.to_a == []. Rails goes a bit further and adds #blank?, which is handy for things that might be nil or empty strings.

I never learned Objective-C, but I just read that in that language:

"NULL is a void *, nil is an id, and Nil is a Class pointer"

...and apparently there is also NSNull.

https://nshipster.com/nil/

Fascinating. I wrote objective-c for years and cannot recall ever encountering the proper-noun form of Nil.

The other three are quite common.

https://stackoverflow.com/questions/59437282/can-i-use-null-...

TL;DR: 0 is always NULL, but NULL is not always 0. Checking or assigning a pointer to 0 will work but converting NULL to an integer is implementation-defined.

https://en.wikipedia.org/wiki/Wonowon,_British_Columbia

I tried to figure out the what3words value for the location but can't find a search term it likes.

Back when I was a network engineer I liked to imagine that I sent a lot of bad traffic there.

I was just in Sierra Leone last week and I was telling my brother about this place.

Also, null might be the empty string, but when is it ever zero?

Edit: this is a serious question.

A language that truly supports null has monadic types, meaning that typed value (scalar, string, object, etc) or something else is specifically tracked (null, undefined, etc). Languages that do not natively support that often have developers that cheat, where they assign some particular value to represent null. Commonly, this is 0 or -1 in numbers and an empty or literal "null" in strings. This works fine unless these values appear actually as legitimate values.

Lately, I program in a language that has distinct concepts of Null and Empty and Nothing and the empty string ("") and arrays that are not Empty but contain zero elements. And of course NUL characters.

This is obviously at least five times as good as just having one option for null.

> arrays that are not Empty but contain zero elements

What is an array that is not empty but contains zero elements?

Well, Empty is a special value in VBA. And I forgot to mention, there are two kinds of "empty" arrays that are not Empty. So it's six times as good as a normal language.

Here's an example:

    ' x can be anything, including an array, but
    ' defaults to the value Empty.
    Dim x

    ' y is an array of values that can be anything,
    ' which defaults to an empty array.
    Dim y()
    
    ' Initialize x as an empty array
    x = Array()
    
    ' The following two statements print 0 and -1.
    Debug.Print LBound(x)
    Debug.Print UBound(x)
    
    ' The following two statements error with
    ' "Subscript out of range" even though y
    ' is also a kind of empty array.
    Debug.Print LBound(y)
    Debug.Print UBound(y)

IIRC in Visual Basic these are arrays with lower bound bigger than upper bound.

...but sometimes you can observe this and sometimes you can't.

Sounds like a trick question. How about the array of the largest number?

Which language?

You can look at headers:

#define NULL 0 //C++

#define NULL ((void*)0) //C

I think later versions of C++ do something...different, but I’m not up to date enough to know without looking it up.

Ok, I wasn't thinking of C, but even so, isn't NULL a pointer value, not an integer? If you're treating a null pointer as an integer zero, something's gone very wrong.

Also I think I vaguely remember from discussions about the standards, that a NULL pointer is not guaranteed to be numerically equal to zero in a standards compliant compiler.

But yeah, I was thinking of database NULLs.

C++03 and earlier stipulate that literal 0 is always the null pointer, whether it really is on any given hardware or not. C++11 and later deprecate this and introduce a new keyword `nullptr`.

edit: Also, null is not an empty string. The null character that terminates a string is unrelated to null pointers.

Normally I call it the NUL character to distinguish it.

In Oracle SQL, an empty string is equivalent to a null, as I recall. However, that is not true for all databases.

Man, this is one of those discussions I’d like to drag out for a little bit, but unfortunately not in a position to do so. I will leave you with the idea that null can indeed be a value, as in a null-terminated string. Go look at that guy in memory.

If you're going to split hairs, I'm going to say a NUL character is obviously not the same concept as a NULL in general, nor is it a number that you'd use for a coordinate.

The definition of NULL is technically machine-dependent in C. It happens to be 0 on (almost?) every machine, but that's not guaranteed. In C++ it's guaranteed to be 0.

The times where it wasn't zero are interesting, https://stackoverflow.com/questions/2597142/when-was-the-nul...

"May you live in interesting times!"

It's a fair point.

Null is the absence of a value. When used in a programming context it is either a pointer (which is not an integer or a float -- it's the pointer to the absence of an integer or a float. It is not equivalent to 0 or 0.0 or ""), a magic number (specifically for chars), or a special structure with a flag.

This more correctly would be "Default=0 Island". A database that doesn't have a nullable field would be the one where you'd have 0.0 as the defaults.

>It's a fair point.

Pun.

When it's a pointer.

Remember, a pointer contains the actual address in RAM, or 0 when the pointer is null.

Usually, but not always.

It would be cooler to call it Fernando Poo[1].

[1] https://illuminatus.fandom.com/wiki/Fernando_Poo

Would it though?

The Illuminatus! Trilogy is all about #Winning.

Each language can define NULL differently. However, because eventually it gets compiled to machine code, it does indeed need to be represented by some value. Most languages represent that value as 0, but not always.

It's better to think about NULL as a value plus a type. The value "False" may be 0 with a boolean type, just as NULL may be 0 with a pointer type.

Golang has typed nil pointers (that is, a nil *CustomError is not equal to a nil error and so on) and it is probably the single thing that has bitten me the most in go.

Null is also the absence of a value altogether.

> Null is also the absence of a value altogether.

In digital logic, there is no such thing as an "absence of a value". Everything must be represented as bits one way or another. Computers can certainly represent higher level concepts like an "absence of value", but at the lowest levels, they must be represented by some bit-stream. Types are generally the way that higher level concepts can be translated from low-level bitstreams.

There certainly can be an absence of value if the value isn't there. Think serialization or sparse arrays. A null may be represented by the absence of representation.

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