I am using a MixHash to combine two Hashes with the Bag add (+) operator. This seems to work - but ... I am a bit surprised that the result of the union needs to be re-coerced back to a MixHash.
My guess is that the Bag add (+) infix operator coerces everything to a Bag first and returns the result as a Bag. This may be risky for me as some of my weights are negative (thus the Mix in the first place). Will this properly add negative weights?
Alternatively, is there a Mix add (+) operator?
my MixHash $dim-mix;
for ... {
my $add-mix = $!dims.MixHash;
$dim-mix = $dim-mix ?? ( $dim-mix (+) $add-mix ).MixHash !! $add-mix;
}
dd $dim-mix;
Now I look at this paraphrased code, perhaps there is some formulation of ternary ?? !! that can avoid spelling out $dim-mix in the test since already on the left?
Many thanks for any advice!
my $add-mix = (foo => 0.22, bar => -0.1).Mix;
my $dim-mix;
for ^5 {
$dim-mix (+)= $add-mix;
}
dd $dim-mix; # Mix $dim-mix = ("foo"=>1.1,"bar"=>-0.5).Mix
Obviously I've not used a MixHash, but you can sort that out if you need to after the loop.
(And of course you might be thinking "but isn't a Mix immutable?" It is -- but you have to distinguish variables and values. $dim-mix is a variable, a Scalar variable. Even if you type it -- my Mix $dim-mix; it's still a Scalar variable holding a Mix value. You can always assign to a Scalar.)
I'm starting to get a routine for questions like this where I don't know what's going on but I think I ought to be able to figure it out. Here was my process:
I got your code to run to see what it did. I tried to simplify the ternary. Hmm.
I turned to the doc. There was the doc page for (+). That called it "Baggy addition". That was worrisome given that a Bag only holds (positive) integers.
I turned to the source. I fired off a search of the rakudo sources for "Baggy addition". One result. I focused on the multi with (Mixy:D $a, QuantHash:D $b) signature. This showed me that the result should stay Mixy, i.e. the doc's implication it would or could go Baggy is a red herring.
I returned to the code and started wondering what I could do. When I initially tried to use (+)= to simplify the main assignment the compiler complained expected MixHash but got Mix. I tried a half dozen things that didn't work then just changed the MixHash constraint on $dim-mix to Mixy and it worked.
Then I thought through what was going on and realized that almost all the types were getting in the way of P6 just doing the right thing.
You can add some types back in if you really need them.
(But do you really need them? When types are absolutely necessary they're great. Otherwise, imo, think twice, and then twice again, before introducing them. They can easily make code harder to read, reason about, compose, and slower.)
(Of course there are occasions on which they're not strictly necessary but do really help overall. Imo, as with all things, keep it simple at first and only complexify if you see clear benefits for a particular line of code.)
Okay, what I really wanted to do is, I have an Array and I want to choose a random element from it. The obvious thing to do is get an integer from a random number generator between 0 and the length minus 1, which I have working already, and then applying Array.get, but that returns a Maybe a. (It appears there's also a package function that does the same thing.) Coming from Haskell, I get the type significance that it's protecting me from the case where my index was out of range, but I have control over the index and don't expect that to happen, so I'd just like to assume I got a Just something and somewhat forcibly convert to a. In Haskell this would be fromJust or, if I was feeling verbose, fromMaybe (error "some message"). How should I do this in Elm?
I found a discussion on the mailing list that seems to be discussing this, but it's been a while and I don't see the function I want in the standard library where the discussion suggests it would be.
Here are some pretty unsatisfying potential solutions I found so far:
Just use withDefault. I do have a default value of a available, but I don't like this as it gives the completely wrong meaning to my code and will probably make debugging harder down the road.
Do some fiddling with ports to interface with Javascript and get an exception thrown there if it's Nothing. I haven't carefully investigated how this works yet, but apparently it's possible. But this just seems to mix up too many dependencies for what would otherwise be simple pure Elm.
(answering my own question)
I found two more-satisfying solutions:
Roll my own partially defined function, which was referenced elsewhere in the linked discussion. But the code kind of feels incomplete this way (I'd hope the compiler would warn me about incomplete pattern matches some day) and the error message is still unclear.
Pattern-match and use Debug.crash if it's a Nothing. This appears similar to Haskell's error and is the solution I'm leaning towards right now.
import Debug
fromJust : Maybe a -> a
fromJust x = case x of
Just y -> y
Nothing -> Debug.crash "error: fromJust Nothing"
(Still, the module name and description also make me hesitate because it doesn't seem like the "right" method intended for my purposes; I want to indicate true programmer error instead of mere debugging.)
Solution
The existence or use of a fromJust or equivalent function is actually code smell and tells you that the API has not been designed correctly. The problem is that you're attempting to make a decision on what to do before you have the information to do it. You can think of this in two cases:
If you know what you're supposed to do with Nothing, then the solution is simple: use withDefault. This will become obvious when you're looking at the right point in your code.
If you don't know what you're supposed to do in the case where you have Nothing, but you still want to make a change, then you need a different way of doing so. Instead of pulling the value out of the Maybe use Maybe.map to change the value while keeping the Maybe. As an example, let's say you're doing the following:
foo : Maybe Int -> Int
foo maybeVal =
let
innerVal = fromJust maybeVal
in
innerVal + 2
Instead, you'll want this:
foo : Maybe Int -> Maybe Int
foo maybeVal =
Maybe.map (\innerVal -> innerVal + 2) maybeVal
Notice that the change you wanted is still done in this case, you've simply not handled the case where you have a Nothing. You can now pass this value up and down the call chain until you've hit a place where it's natural to use withDefault to get rid of the Maybe.
What's happened is that we've separated the concerns of "How do I change this value" and "What do I do when it doesn't exist?". We deal with the former using Maybe.map and the latter with Maybe.withDefault.
Caveat
There are a small number of cases where you simply know that you have a Just value and need to eliminate it using fromJust as you described, but those cases should be few and far between. There's quite a few that actually have a simpler alternative.
Example: Attempting to filter a list and get the value out.
Let's say you have a list of Maybes that you want the values of. A common strategy might be:
foo : List (Maybe a) -> List a
foo hasAnything =
let
onlyHasJustValues = List.filter Maybe.isJust hasAnything
onlyHasRealValues = List.map fromJust onlyHasJustValues
in
onlyHasRealValues
Turns out that even in this case, there are clean ways to avoid fromJust. Most languages with a collection that has a map and a filter have a method to filter using a Maybe built in. Haskell has Maybe.mapMaybe, Scala has flatMap, and Elm has List.filterMap. This transforms your code into:
foo : List (Maybe a) -> List a
foo hasAnything =
let
onlyHasRealValues = List.filterMap (\x -> x) hasAnything
in
onlyHasRealValues
Do you think x, y, z are good variable names? How will you explain a new programmer to write readable code?
Readable code means some combination of comments and variable and function naming that allows me to read the code once and understand it. If I have to read it more than once, or spend my time working through complicated loops or functions, there's room for improvement.
Good summary descriptions at the top of files and classes are useful to give the reader context and background information.
Clear names are important. Verbose names make it much easier to write readable code with far fewer comments.
Writing readable code is a skill that takes some time to learn. I personally like overly verbose names because they create self documenting code.
As already stated x, y, and z are good variables for 3D coordinates but probably bad for anything else...
If someone does not believe that names are important, just use a code obfuscator on some code then ask them to debug it :-).
(BTW that's the only situation where a code obfuscator can be useful IMHO)
There seems to be slightly different conventions per progamming language; however, the consensus these days is to...
use pascal case
make the name meaningful
end with a noun
Here is a decent recap of what Microsoft publishes as standard naming conventions for .NET
The inventor of python has published a style guide which includes naming conventions.
There was a time when Microsoft VC++ developers (myself included) actually rallied around what was known as Hungarian Notation
Certainly there are multiple schools of thought on this, but I would only use these for counters, and advise far more descriptive names for any other variables.
x, y and z can be perfectly good variable names. For example you might be writing code that refers to them in reference to a 3D cartesian coordinate system. These names are often used for the three axes in such a system and as such they would be well suited.
I would give them some maintenance work on some code with variables called x, y, z and let them realise for themselves that readability is vital...
95% of code viewing is not by the author, but by the customer that everyone forgets about - the next programmer. You owe it to her to make her life easy.
Good variable names describe exactly what they are without being overly complex. I always use descriptive names, even in loops (for instance, index instead of i). It helps keep track of what's going on, especially when I'm working on rewriting a particularly complex piece of code.
Well give them a chunk of bad code and ask them to debug it.
Take the following code (simple example)
<?php $a = fopen('/path/to/file.ext', 'w');$b = "NEW LINE\n";fwrite($a, $b);fclose($a);?>
The bug is: File only ever contains 1 line when it should be a log
Problem: 'w' in fopen should be 'a'
This obviously is a super easy example, if you want to give them a bigger more complicated example give them the WMD source and ask them to give you readable code in 2 hours, it will get your point across.
As long as x, y and z are (3D) Cartesian co-ordinates, then they're great names.
In a similar vein, i, j and k would be OK for loop variables.
In all cases, the variable names should relate to the data
x,y and z are acceptable variable names if they represent 3d coordinates, or if they're used for iterating over 2 or 3 dimensional arrays.
This code is fine as far as I'm concerned:
for(int x = 0; x < xsize ; x++)
{
for(int y = 0; y < ysize ; y++)
{
for(int z = 0; z < zsize ; z++)
{
DoSomething(data[x][y][z]);
...
This one is a short answer, but it works very well for me:
If it would need a code comment to describe it, then rethink the variable name.
So if it's obvious, why "x" was choosen, then they are good names. E.g. "i" as variable name in a loop is (often) pretty obvious.
An ideal variable name is both short (to make the code more compact) and descriptive (to help understanding the code).
Opinions differ on which of the two is more important. Personally, I'd say it depends on the scope of the variable. A variable used only inside a 3 line loop can get away with being single letter. A class field in a 500 line class better be pretty damn descriptive. The Spartan Programming philosophy says that as far as possible, all units of code should be small enough that variable names can be very short.
Readable code and good naming conventions are not the same thing!
A good name for a variable is one that allows you to understand (or reasonably guess) the purpose and type of the variable WITHOUT seeing the context in which it is used. Thus, "x" "y" and "z" say coordinates because that is a reasonable guess. Conversely, a bad name is one that leads you to a wrong likely guess. For example, if "x" "y" and "z" represent people.
A good name for a function is one that conveys everything you would need to know about it without having to consult its documentation. That is not always possible.
Readable code is first of all code whose structured could be understood even if you obfuscated all variable and function names. If you do that and can't figure out the control structure easily, you're screwed.
Once you have readable code and good naming, then maybe you'll have truly readable code.
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Closed 9 years ago.
This question is to seek out good examples of Hungarian Notation, so we can bring together a collection of these.
Edit: I agree that Hungarian for types isn't that necessary, I'm hoping for more specific examples where it increases readability and maintainability, like Joel gives in his article (as per my answer).
The problem with asking for good examples of Hungarian Notation is that everyone's going to have their own idea of what a good example looks like. My personal opinion is that the best Hungarian Notation is no Hungarian Notation. The notation was originally meant to denote the intended usage of a variable rather than its type but it's usually used for type information, particularly for Form controls (e.g., txtFirstName for a text box for someone's first name.). This makes the code less maintainable, in terms of readability (e.g., "prepIn nounTerms prepOf nounReadability") and refactoring for when the type needs to be changed (there are "lParams" in the Win32 API that have changed type).
You should probably consider not using it at all. Examples:
strFirstName - this can just be firstName since it's obvious what it's for, the type isn't that important and should be obvious in this case. If not obvious, the IDE can help you with that.
txtFirstName - this can change to FirstNameTextBox or FirstName_TextBox. It reads better and you know it's a control and not just the text.
CAccount - C was used for class names in MFC but you really don't need it. Account is good enough. The uppercase name is the standard convention for types (and they only appear in specific places so they won't get confused with properties or methods)
ixArray (index to array) - ix is a bit obscure. Try arrayIndex.
usState (unsafe string for State) - looks like "U.S. State". Better go with state_UnsafeString or something. Maybe even wrap it in an UnsafeString class to at least make it type-safe.
The now classic article, as mentioned in other Hungarian posts, is the one from Joel's site:
http://www.joelonsoftware.com/articles/Wrong.html
p
(for pointer). Its pretty much the only prefix I use. I think it adds a lot to a variable (eg that its a pointer) and so should be treated a little more respectfully.
Hungarian for datatypes is somewhat passe now IDEs can tell you what the type is (in only a few seconds hovering over the variable name), so its not so important. But treating a pointer as if its data is not good, so you want to make sure it's obvious to the user what it is even if he makes assumptions he shouldn't when coding.
t
Tainted data. Prefix all data incoming from an untrusted source to make that variable as tainted. All tainted data should be cleansed before any real work is done on it.
It's pointless to use Hungarian to indicate types because the compiler already does it for you.
Where Hungarian is useful is to distinguish between logically different sorts of variables that have the same raw type. For example, if you are using ints to represent coordinates, you could prefix x coordinates with x, y coordinates with y and distances with d. So you would have code that looks like
dxHighlight = xStart - xEnd
yHighlight = yLocation + 3
yEnd = yStart + dyHeight
dyCode = dyField * 2
and so on. It's useful because you can spot errors at a glance: If you add a dy to a y, you always get a y. If you subtract two x's you always get a dx. If you multiply a dy by a scalar, you always get a dy. And so on. If you see a line like
yTop = dyText + xButton
you know at a glance that it is wrong because adding a dy and a x does not make sense. The compiler could not catch this for you because as far as it can tell, you are adding an int to an int which is fine.
Do not use language specific prefixes.
We use:
n: Number
p: Percentage 1=100% (for interest rates etc)
c: Currency
s: String
d: date
e: enumeration
o: object (Customer oCustomer=new Customer();)
...
We use the same system for all languages:
SQL
C
C#
Javascript
VB6
VB.net
...
It is a life saver.
Devil's Advocate: The best example of Hungarian notation is not to use it. :D
We do not gain any advantage to using Hungarian notation with modern IDEs because they know the type. It adds work when refactoring a type for a variable since the name would also have to be changed (and most of the time when you are dealing with a variable you know what type it is anyway).
You can also get into ordering issues with the notation. If you use p for pointer and a for address do you call your variable apStreet or paStreet? Readability is diminished when you don't have consistency, and you have to use up valuable mind space when you have to remember the order that you have to write the notation in.
I find hungarian notation can sometimes be useful in dynamic languages. I'm specifically thinking of Server Side Actionscript (essentially just javascript), but it could apply elsewhere. Since there's no real type information at all, hungarian notation can sometimes help make things a bit easier to understand.
Hungarian notation (camel casing, as I learned it) is invaluable when you're inheriting a software project.
Yes, you can 'hover' over a variable with your IDE and find out what class it is, but if you're paging through several thousand lines of code you don't want to have to stop for those few seconds - every.... single.... time....
Remember - you're not writing code for you or your team alone. You're also writing it for the person who has to pick up this code 2-5 years down the road and enhance it.
I was strongly against Hungarian notation until I really started reading about it and trying to understand it's original intent.
After reading Joels post "Wrong" and the article "Rediscovering Hungarian Notation" I really changed my mind. Done correct I belive it must be extremly powerful.
Wrong by Joel Spolsky
http://www.joelonsoftware.com/articles/Wrong.html
Rediscovering Hungarian Notation
http://codingthriller.blogspot.com/2007/11/rediscovering-hungarian-notation.html
I belive that most Naysayers have never tried it for real and do not truly understand it.
I would love to try it out in a real project.
I think the key thing to take away from Joel's article, linked above, and Hungarian Notation in general, is to use it when there's something non-obvious about the variable.
One example, from the article, is encoded vs non encoded strings, it's not that you should use hungarian 'us' for unsafe strings and 's' for safe strings, it's that you should have some identifier to indicate that a string is either safe or not. If it becomes standard, it becomes easy to see when the standard is being broken.
The only Hungarian that's really useful anymore is m_ for member variables. (I also use sm_ for static members, because that's the "other" scope that still exists.) With widescreen monitors and compilers that take eight-billion-character-long variable names, abbreviating type names just isn't worth it.
m
When using an ORM (such as hibernate) you tend to deal managed and unmanaged objects. Changing an managed object will be reflected in the database without calling an explicit save, while dealing with a managaged object requires an explicit save call. How you deal with the object will be different depending on which it is.
I find that the only helpful point is when declaring interface controls, txtUsername, txtPassword, ddlBirthMonth. It isn't perfect, but it helps on large forms/projects.
I don't use it for variables or other items, just controls.
In addition to using 'p' for pointer, I like the idea of using 'cb' and 'cch' to indicate whether a buffer size parameter (or variable) is a count of bytes or a character count (I've also seen - rarely - 'ce' used to indicate a count of elements). So instead of conveying type, the prefix conveys use or intent.
I admit, I don't use the prefix as consistently as I probably should, but I like the idea.
A very old question, but here's a couple of "Hungarian" prefixes I use regularly:
my
for local variables, to distinguish locality where the name might make sense in a global context. If you see myFoo, it's only used in this function, regardless of anything else we do with Foos anywhere else.
myStart = GetTime();
doComplicatedOperations();
print (GetTime() - myStart);
and
tmp
for temporary copies of values in loops or multi-step operations. If you see two tmpFoo variables more than a couple of lines from each other, they're almost certainly unrelated.
tmpX = X;
tmpY = Y;
X = someCalc(tmpX, tmpY);
Y = otherCalc(tmpX, tmpY);
and sometimes old and new in for similar reasons to tmp, usually in longer loops or functions.
Well, I use it only with window control variables. I use btn_, txt_, lbl_ etc to spot them. I also find it helpful to look up the control's name by typing its type (btn_ etc).
I only ever use p for a pointer, and that's it. And that's only if I'm in C++. In C# I don't use any hungarian notation.
e.g.
MyClass myClass;
MyClass* pMyClass;
That's all :)
Edit: Oh, I just realised that's a lie. I use "m_" for member variables too. e.g.
class
{
private:
bool m_myVar;
}
I agree that Hungarian notation is no longer particularly useful. I thought that its original intention was to indicate not datatype, but rather entity type. In a code section involving the names of customers, employees and the user, for example, you could name local string variables cusName, empName and usrName. That would help distinguish among similar-sounding variable names. The same prefixes for the entities would be used throughout the application. However, when OO is used, and you're dealing with objects, those prefixes are redundant in Customer.Name, Employee.Name and User.Name.
The name of the variable should describe what it is. Good variable naming makes Hungarian notation useless.
However, sometimes you'd use Hungarian notation in addition to good variable naming. m_numObjects has two "prefixes:" m_ and num. m_ indicates the scope: it's a data member tied to this. num indicates what the value is.
I don't feel hindered at all when I read "good" code, even if it does contain some "Hungarian." Right: I read code, I don't click it. (In fact, I hardly use my mouse ever when coding, or any voodoo programming-specific lookup features.)
I am slowed when I read things like m_ubScale (yes, I'm looking at you, Liran!), as I have to look at its usage (no comments!) to find out what it scales (if at all?) and it's datatype (which happens to be a fixed-point char). A better name would be m_scaleFactor or m_zoomFactor, with a comment as a fixed-point number, or even a typedef. (In fact, a typedef would be useful, as there are several other members of several classes which use the same fixed-point format. However, some don't, but are still labeled m_ubWhatever! Confusing, to say the least.)
I think Hungarian was meant to be an additive to the variable name, not a replacement for information. Also, many times Hungarian notation adds nothing at all to the variable's readability, wasting bytes and read time.
Just my 2¢.
There's no such thing as a good example of hungarian notation. Just don't use it. Not even if you are using a weakly typed language. You'll live happier.
But if you really need some reason not to use it, this is my favourite one, extracted from this great link:
One followon trick in the Hungarian notation is "change the type of a variable but leave the variable name unchanged". This is almost invariably done in windows apps with the migration from Win16 :- WndProc(HWND hW, WORD wMsg, WORD wParam, LONG lParam) to Win32 WndProc(HWND hW, UINT wMsg, WPARAM wParam, LPARAM lParam) where the w values hint that they are words, but they really refer to longs. The real value of this approach comes clear with the Win64 migration, when the parameters will be 64 bits wide, but the old "w" and "l" prefixes will remain forever.
I find myself using 'w' meaning 'working', as a prefix instead of 'temp' or 'tmp', for local variables that are just there to jockey data around, like:
Public Function ArrayFromDJRange(rangename As Range, slots As Integer) As Variant
' this function copies a Disjoint Range of specified size into a Variant Array 7/8/09 ljr
Dim j As Integer
Dim wArray As Variant
Dim rCell As Range
wArray = rangename.Value ' to initialize the working Array
ReDim wArray(0, slots - 1) ' set to size of range
j = 0
For Each rCell In rangename
wArray(0, j) = rCell.Value
j = j + 1
Next rCell
ArrayFromDJRange = wArray
End Function
In this question, a user commented to never use the With block in VB. Why?
"Never" is a strong word.
I think it fine as long as you don't abuse it (like nesting)
IMHO - this is better:
With MyCommand.Parameters
.Count = 1
.Item(0).ParameterName = "#baz"
.Item(0).Value = fuz
End With
Than:
MyCommand.Parameters.Count = 1
MyCommand.Parameters.Item(0).ParameterName = "#baz"
MyCommand.Parameters.Item(0).Value = fuz
There is nothing wrong about the With keyword. It's true that it may reduce readibility when nested but the solution is simply don't use nested With.
There may be namespace problems in Delphi, which doesn't enforce a leading dot but that issue simply doesn't exist in VB.NET so the people that are posting rants about Delphi are losing their time in this question.
I think the real reason many people don't like the With keyword is that is not included in C* languages and many programmers automatically think that every feature not included in his/her favourite language is bad.
It's just not helpful compared to other options.
If you really miss it you can create a one or two character alias for your object instead. The alias only takes one line to setup, rather than two for the With block (With + End With lines).
The alias also gives you a quick mouse-over reference for the type of the variable. It provides a hook for the IDE to help you jump back to the top of the block if you want (though if the block is that large you have other problems). It can be passed as an argument to functions. And you can use it to reference an index property.
So we have an alternative that gives more function with less code.
Also see this question:
Why is the with() construct not included in C#, when it is really cool in VB.NET?
The with keyword is only sideswiped in a passing reference here in an hilarious article by the wonderful Verity Stob, but it's worth it for the vitriol: See the paragraph that starts
While we are on identifier confusion. The with keyword...
Worth reading the entire article!
The With keyword also provides another benefit - the object(s) in the With statement only need to be "qualified" once, which can improve performance. Check out the information on MSDN here:
http://msdn.microsoft.com/en-us/library/wc500chb(VS.80).aspx
So by all means, use it.