[RESOLVED} Getting compiler error when using Defined values

[Joacim Andersson]

I have this in a scripts header file:

Code: ags

#define PLAYER_ON_PORTAL 13;

Then elsewhere I have this:

Code: ags

function PlayerOnPortal()
{
  Object* portal = Object.GetByName("oPortal");
  if (portal != null)
  {
    if (Object.GetAtRoomXY(player.x, player.y) == portal)
    {
      player.StopMoving();
      player.FaceDirection(eDirectionDown, eBlock);
      CallRoomScript(PLAYER_ON_PORTAL); 
    }
  }
}

If I replace the line CallRoomScript(PLAYER_ON_PORTAL) to CallRoomScript(13) it works, but when I try to use the defined value I get "Parse error in expr. near '13', so the parser has replaced the PLAYER_ON_PORTAL macro with the value 13, yet it doesn't work. Any help?

[eri0o]

Remove the trailing ; character, define is a text macro replacement, you are placing a ; inside the function parameter.

[Joacim Andersson]

Oh, yes. of course! Thank you. You know I started my development career as a C/C++ developer, I should know this stuff, but I think I just added the trailing semicolon out of habit. Yet I have several defined macros above this line with no trailing semicolons.

[eri0o]

For this case specifically you can also use an enum instead, enum can fakely be a const int or typedef like in feelings. You just can't use an enum for non-dynamic array size.

In ags4 with the new compiler, I believe readonly is the keyword you use for const like behavior. And there I believe that it also works in non-dynamic array size.

[Crimson Wizard]

In ags4 with the new compiler, I believe readonly is the keyword you use for const like behavior. And there I believe that it also works in non-dynamic array size.

AGS 4 supports both "const" and "readonly",
where "const" is a compile-time constant, and it is replaced with actual value during compilation;
while "readonly" is a runtime-time constant, meaning it may be initialized by any expression, including calling a function, which result can be only calculated at runtime.

[Joacim Andersson]

"readonly" is a runtime-time constant, meaning it may be initialized by any expression, including calling a function, which result can be only calculated at runtime.

So does that mean that a readonly can be initialized once, much like a readonly in C# can be initialized in the constructor. However, since AGS doesn't have classes and constructors, does that mean that a readonly is not initialized when created like a normal int is initialized to 0?

[eri0o]

I think that it's simply single assignment - in ags4.

You may have readonly global variables, local variables, function parameters, and struct attributes.

Two most common uses of a readonly variable are function parameters and local variables. This works as a "failproof" method to ensure that they are only assigned, but are never changed within the function by programmer's mistake.

In ags4 managed structs will have constructors soon - CW has a PR with them already.

[Crimson Wizard]

So does that mean that a readonly can be initialized once, much like a readonly in C# can be initialized in the constructor. However, since AGS doesn't have classes and constructors, does that mean that a readonly is not initialized when created like a normal int is initialized to 0?

AGS has "structs", which are like something in between struct and class in functionality.
But you are right that it does not have constructors just yet. There will be soon in AGS 4.0 though (we're working on that).

Traditional use of "readonly" in structs was for attributes (aka properties). That would make these gettable but not settable.

This may be done in 3.* already, and is thoroughly used in standard engine API:

Example of user script:

Code: ags

struct MyStruct
{
    import void InitMe(int data);
    import readonly attribute int Data;

    protected int _data;
};

Code: ags

void MyStruct::InitMe(int data)
{
     _data = data;
}

int MyStruct::get_Data()
{
    return _data;
}

[Joacim Andersson]

Will AGS 4 have both getter and setter properties? I would love that, to get rid of all global variables.

[Crimson Wizard]

Will AGS 4 have both getter and setter properties? I would love that, to get rid of all global variables.

AGS already has properties with getters and setters, as well as ways to protect fields of structs from public access

The manual is a bit lacking in regards to this topic unfortunately, but the general explanation may be found here:
https://adventuregamestudio.github.io/ags-manual/OOProgramming.html

[Joacim Andersson]

Yeah ok, so basically you have to create a Get and a Set method (much like Java) but above it looked like the read-only data variable could be read by the int MyStruct::get_Data() method, which isn't declared. So it looks like that would be called when you use
value = myStructInstance.Data
Have I understood that correctly? If so it's still different from having a GetData() and a SetData() method.

[Crimson Wizard]

Yeah ok, so basically you have to create a Get and a Set method (much like Java) but above it looked like the read-only data variable could be read by the int MyStruct::get_Data() method, which isn't declared. So it looks like that would be called when you use

Code: ags

value = myStructInstance.Data

Have I understood that correctly? If so it's still different from having a GetData() and a SetData() method.

Yes, that is correct, if you have declared an attribute Data, then you don't need GetData and SetData methods, but you need to define get_Data and set_Data methods.

I made a small mistake in the example above, in case get_Data was not declared in the struct explicitly, then its definition has to be done using an "extender function" syntax

Code: ags

int get_Data(this MyStruct*)
{
    return this._data;
}

This is also explained in the article that I linked above.

[Joacim Andersson]

You're confusing me, the get_Data and set_Data (or whatever you like to call them) still have to be declared but they are automatically called when you use code like this:

Code: ags

int value = myStructInstance.Data;
value++;
myStructInstance.Data = value;

So you don't have to use this code:

Code: ags

int value = myStructInstance.get_Data();
myStructInstance.set_Date(value * 2);

So basically they work like property getter and setters in C#?

So you can also use extension methods? That's cool. I wish the documentation were a bit more extensive on all of the OOP stuff.

[Joacim Andersson]

Does Lambda functions also exist?

[Crimson Wizard]

So basically they work like property getter and setters in C#?

That is correct.

Does Lambda functions also exist?

No.

[Joacim Andersson]

Thank you so much for your replies and explanations. I promise that this will be my last post in this thread since we got a bit off-topic.

But what is the plan for AGS, will there be more 3.x releases before 4.0 is ready?

I also hope that you guys get constructors to work properly, then I will eagerly await the release of 4.0.

[Crimson Wizard]

I wish the documentation were a bit more extensive on all of the OOP stuff.

Yes it is true, some parts of the manual have unfortunately been neglected for a while. This is mostly because of small number of contributors to the engine.

But what is the plan for AGS, will there be more 3.x releases before 4.0 is ready?

Eventually we'd like to focus on AGS 4, and only do patch releases to 3.x.
AGS 4 has been delayed for too long, because of inconsistent planning...

3.x is a backwards compatible engine which can run many old games. Plus it's a way to upgrade game projects from earlier years, if someone wants to move them to AGS 4 they'd have to go through 3.x first. So it will be around as a backup version.