Beginner to User Defined Data Types (Custom Type, UDTs)

I've decided to learn custom types (I haven't learnt classes yet so I figured I should learn this first). So far I've read this tutorial http://sourcedaddy.com/ms-excel/crea...ata-types.html

The problem is that I can't see anything exceptionally useful about user defined types *; so in case I am overlooking something big, I thought I'd ask the experts.

So how about it? What are the pros and cons that newbies to UDTs should know?






* (using the example on URL provided) I admit that its neat that you can group related variables together but if you named the variables with similar starting prefixes instead of using a custom type that would achieve almost the same result e.g.

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Add 1 Pro = Intellisense is applied when writing code with custom types.

Anything else?

The is nothing exceptional about UDTs. Just as there is nothing exceptional about arrays for dealing with multiple items

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Having said that both can make dealing with certain data much more straightforward.

I use them when simply storing information, such as a bunch of parameters. If I need to manipulate values or provide related method/function then obviously I step up to a class object.

Originally Posted by Izandol

I do not understand what this means. Naming the variables in such a way does not achieve anything.

Naming the variables in such a way achieves better readability of code.

I've written a better example below.
I would rather work with Sub Example1 instead of Sub Example2. The "Car_" prefix makes the code easier to read and easier to note which variables are directly related to "Car"
Sub Example3 (using UDTs) has a slight advantage over Sub Example1 because of the use of Intellisense when writing the code.

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Originally Posted by Izandol

Further if you do not see a difference between a UDT and naming variables I do not think you will like classes.

I do see a difference between using UDTs variables and global variables. I don't see any major advantage.

Actually I have a feeling I will love classes (once I get round to learning them). Certain features of them sound extremely useful.

Thanks for the explanation Kyle. +1

Originally Posted by Kyle123

they can be handy when dealing with data with multiple properties and you can pass them around as parameters

True. On the other hand, I could use global level variables to pass data around instead of using a UDT could I not? As for the data with multiple properties - instead of using a UDT with 5 properties (or whatever they are called in UDTs), I could use 5 global variables.

Originally Posted by Kyle123

tbh I don't usually bother with UDTs, classes are much more useful.

I'm beginning to think of skipping UDTs and jump straight to classes. From what I've read/heard, they are much more useful!

Originally Posted by Izandol

A UDT groups variables into one entity - something like, but not as useful as, a class with just member variables.

I agree that the logical grouping is nice. However see my reply to Kyle. I could use 5 global level variables (with a nice naming prefix ) to pass data instead of a UDT containing 5 variables. Using 5 variables instead of a UDT would mean I wouldn't need to declare the UDT in every sub that requires the variables.


The biggest disadvantage that I see to UDTs is that they don't hold their data. If I use global level variables, they (usually) hold their data from sub to sub. With a UDT, I would need to set their values every time before I can use them. Please correct me if I am wrong on this point.


UPDATE: Thanks to demo code provided by Andy Pope, I went back and tested this in a current project. Both assumptions I made in this reply are wrong. My apologies.

Thanks for the explanation Andy Pope +1

Originally Posted by Andy Pope

The is nothing exceptional about UDTs.

That's what I'm coming to!

Originally Posted by Andy Pope

If I need to manipulate values or provide related method/function then obviously I step up to a class object.

Classes! I must learn Classes!

UPDATE:This summary is outdated. See the last post for the latest version.

I was looking for advantages of UDTs but the more I hear about them, the less I like them.

Disclaimer: I haven't tested all of the below myself. If any assumptions below are incorrect, please let me know so I can update the thread to help other new users to UDTs


DISADVANTAGES:

1. Can't hold values after sub ends (Unlike global variables) (PROVEN FALSE See post #12)
2. Need to declare the UDT in every sub that makes use of the UDTs elements (PROVEN FALSE See post #12)
3. Can't declare new instances of a Type (Unlike Redim Preserve on Arrays) (FALSE. See posts #12 & #18)
4. Speed/Performance impact (TRUE. But.... Minor overhead. Nothing to worry about. See post #18 for demonstration)
5. Difficult to use in an Add-In? (e.g. http://stackoverflow.com/questions/1...-from-an-addin )
6. Difficult to pass in Arrays? (e.g. http://www.vbaexpress.com/forum/show...r-Defined-Type)
7. Difficult to determine whether value assigned to UDT element or not (TRUE. But.... No more than a variable of any other type)
8. No control over values assigned to elements of a Type (TRUE Use Classes instead)
9. Can only hold variables, can't process code (TRUE. But... But neither can standard variables)

ADVANTAGES:

1. Can logically group variables together
2. Can have multiple elements passed by one variable (Arrays do too. But it's easier to read Car.Make instead of varArray(5))
3. Intellisense when writing code

Disadvantage 1. UDT can be public just like any other variable. You just need to scope them in the correct place.

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Disadvantage 2. Again depends on your scope definition

Disadvantage 3. Incorrect, you can redim and redim preserve

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Disadvantage 4. I don't see the use of udt against normal variables having a performance hit. Do you have any evidence of this?

Disadvantage 5. Don't see why, you need to clarify your statement about why they are hard to use in addin.

Disadvantage 6. No they are not.

extends previous code example.

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Disadvantage 7. no more than stanadard variables

Originally Posted by Kyle123

To take your logic to its natural conclusion, why even have functions at all? You wouldn't need them if everything is a global variable..

I'm afraid I'm having trouble following that logic. Functions return a value (usually as a result of a calculation). Variables can only retain a value.

Originally Posted by Kyle123

Scope should be kept as small as possible, have a read here about scope http://www.vb6.us/tutorials/variable-scope, then here (http://www.xtremevbtalk.com/showthread.php?t=201646) about why global variables (as opposed to constants) are bad, or at least why they should really only be used as a last resort..I think you should cover the basics first and understand good programming practice, without understanding scope, I think public and private members of classes will completely pass you by.

You don't need to convince me on the coding practice of keeping scopes as small as possible. That is something that I do practice when coding.
Having said that, I do occasionally use global (well project level ) variables when I need to hold values that will be reused in the same WB session.

Originally Posted by Andy Pope

...

Appreciate your detailed myth busting of UDTs disadvantages. +1
At this rate, I may end up using them after all!

1. (Tests code provided). :eep: Whoa. It's now working! Now why didn't it work in my current project? Will go back, test and report back.
2. As above
3. (dazed) That's incredible. Then what did Chip Pearson mean? See: http://www.cpearson.com/excel/classes.aspx (1/3 down the page - where he describes 3 disadvantages to Type)
4. I was reading about UDTs having a slight impact on code performance. It involved a test that used LenB in Immediate window to measure the size of variables. But I can't remember where I read it and a quick google can't find it again
5. This? http://stackoverflow.com/questions/1...-from-an-addin
6. I have come across a few web pages re UDTs and arrays. Here's one: http://www.vbaexpress.com/forum/show...r-Defined-Type
7. I concur.

UPDATE: 1 & 2 tested in current project. Working fine now. (No idea why it played up previously)

Originally Posted by Izandol

Alas I think you are still confused.

I think I am too Which is why I started this thread.

Re the points - I have updated post #11.

There will be a hit in memory allocation

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reports

UDT 20
KM 4
MAKE 0
MODEL 0
PRICE 8

KM 4
MAKE 0
MODEL 0
PRICE 8

I read the following as being unless you dimension prior to run time you will have to ReDim which in itself has a performance hit. Not that you can not do it.

You must declare all the variables you'll need at design time or you need a dynamic array that is resized with Redim Preserve, an awkward and expensive operation.

The other 2 points stand. because you are only assigning values you can not control what values are used or perform additional operations on the value.

Originally Posted by Andy Pope

...

Thanks for testing I have updated post #11 to record this.

Most of the disadvantages of UDTs (post #11) have now been proven false (Thanks to Andy Pope). At this point, I'm now convinced of the usefulness of UDTs.

I won't close this thread yet as there are two "disadvantages" that have not been proven either way. (Disadvantage #5 & #6) I'd be interested if anyone can prove/disprove these.

Originally Posted by Izandol

It would be simple to provide the updated #11 as a new post rather than change the original. I do not know what your actual questions are for points 5 and 6 or maybe I must Goto another forum to figure this out? (perhaps I Resume Next question instead)

LOL

(I prefer thinking of the post references as calls to other subs rather than GoTos! )

UPDATE:This summary is outdated. See the last post for the latest version.

Updated summary below. As requested by Izandol.


DISADVANTAGES:

1. Can't hold values after sub ends (FALSE)
2. Need to declare the UDT in every sub that makes use of the UDTs elements (FALSE)
3. Can't declare new instances of a Type (Unlike Redim Preserve on Arrays) (FALSE)
4. Speed/Performance impact (TRUE. But.... Minor overhead. Nothing to worry about)
5. Difficult to use in an Add-In? (e.g. see http://stackoverflow.com/questions/1...-from-an-addin )
6. Difficult to pass in Arrays? (e.g. see http://www.vbaexpress.com/forum/show...r-Defined-Type)
7. Difficult to determine whether value assigned to UDT element or not (TRUE. But.... No more than a variable of any other type)
8. No control over values assigned to elements of a Type (TRUE Use Classes instead)
9. Can only hold variables, can't process code (TRUE. But... But neither can standard variables)

ADVANTAGES:

1. Can logically group variables together
2. Can have multiple elements passed by one variable (Arrays do too. But it's easier to read Car.Make instead of varArray(5))
3. Intellisense when writing code

Updated summary below. Only Disadvantage #1 is not proved/disproved.


ADVANTAGES:

1. Can logically group variables together
2. Can have multiple elements passed by one variable (Arrays do too. But it's easier to read Car.Make instead of varArray(5))
3. Intellisense when writing code

DISADVANTAGES:

1. Difficult to use in an Add-In? (e.g. see http://stackoverflow.com/questions/1...-from-an-addin )
2. Speed/Performance impact (TRUE. But.... Minor overhead. Nothing to worry about)
3. Difficult to determine whether value assigned to UDT element or not (TRUE. But.... No more than a variable of any other type)
4. Can only hold variables, can't process code (TRUE. But... But neither can standard variables)
5. No control over values assigned to elements of a Type (TRUE Use Classes instead)

MYTHS:

1. Can't hold values after sub ends (FALSE)
2. Need to declare the UDT in every sub that makes use of the UDTs elements (FALSE)
3. Can't declare new instances of a Type (Unlike Redim Preserve on Arrays) (FALSE)
4. Difficult to pass in Arrays? (FALSE)