Type, Class or Module?

Discussion in 'Teaching Programming with B4X' started by wonder, Nov 5, 2016.

  1. wonder

    wonder Expert Licensed User

    In order to choose the right one for you, ask yourself these simple questions:
    1) Will my object contain functions? YES: Class or Module | NO: Type
    2) Will there be more than one instance of my object? YES: Class or Type | NO: Module

    So...
    NO, NO: Type
    NO, YES: Type
    YES, NO: Module
    YES, YES: Class

    Happy programming! :)
     
  2. Enrique Gonzalez R

    Enrique Gonzalez R Well-Known Member Licensed User

    Types are also useful for B4X language because by storing them on a list, you can order them with this specific function:

    Code:
    Type Person (name As String, age As Int)

        
    Dim listOfPersons As List
        listOfPersons.Initialize
      
        listOfPersons.SortType(
    "age",True)
     
  3. LucaMs

    LucaMs Expert Licensed User

    I don't agree completely, although your concepts are valid.

    1) Mainly you should use classes when you need to represent an object, real object or immaterial object.
    2) You can use a single instance of a class instead of a code module; so, if later you will need typical characteristics of classes you are ready to add them.
    3) Types can be useful but a class can be used for the same purpose with more power and control (you can validate the values and also raise events)

    Surely it is easier and faster, sometimes, to write:
    Code:
    Type tPoint(X As Int, Y As Int)
    Anyway a class is better, even in cases like this one.

    Microsoft, after many releases of its products, decided that all things in its languages should be an object, an instance of a class. To me it seems right.
     
    Last edited: Nov 6, 2016
    wonder and inakigarm like this.
  4. Erel

    Erel Administrator Staff Member Licensed User

    I mostly agree with Luca.

    Classes vs modules

    Classes are preferable over static modules in most cases.
    - You are not limited to a single instance.
    - In B4A classes can handle events while code modules cannot (this is not true in B4J and B4i).

    Code modules are useful for utility methods.

    Types vs classes

    Types have two important advantages:
    - Very simple to create.
    - They are serializable with B4XSerializator. This means that you can very easily store the data in a file (or database) or send it over the network.
     
  5. LucaMs

    LucaMs Expert Licensed User

    "Someone" ;) might invent something like TAB after Sub, which shows... (you know) to get automatically a skeleton of property.


    This is very important (and my previous comment shows that I did not know or, more likely, I'd forgotten)
     
    Last edited: Nov 6, 2016
    wonder likes this.
  6. wonder

    wonder Expert Licensed User

    I'm glad I've started this discussion, today I've learned a thing or two... ;)
     
    LucaMs likes this.
  7. thedesolatesoul

    thedesolatesoul Expert Licensed User

    I slightly disagree with serializing types using a generic serializer. I've had many issues in the past specifically related to types inside a list (that i cant remember). One of them was the packagename being written with the type making it unportable. But anyway those were just implementation issues.
    The one problem with a type is that once you serialize it, and and later you need to add a new field to it, it makes the de-serializer non-generic in order to maintain backwards compatibility. Its easier to do with JSON/Dictionaries instead of hardened types.
     
  8. Erel

    Erel Administrator Staff Member Licensed User

    B4XSerializator deals with missing fields and also deals with different package names (in that case the types must be declared in the Main module).

    There are two types of usages for B4XSerializator:
    - Communication with another process or device.
    - Persisting data.

    In the later case you do need to plan ahead and decide how will your code deal with future changes. For example you can add a version field to the custom type.
     
    Last edited: Nov 7, 2016
  9. thedesolatesoul

    thedesolatesoul Expert Licensed User

    Cool, thats great to know.
    A few years too late for me though ;)
     
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