The Point type

[Simon Knight]

I am reviewing the LCB file that Bernd kindly published in order to try and get some understanding of how a widget is created.

In the code the type Point is used e.g.

Code: Select all

  private variable mCenterPoint as Point

Where is this type documented ?
Looking in the LCB dictionary the following types are defined :

The range of core types is relatively small, comprising the following:

nothing: the single value nothing
Boolean: one of true or false
Integer: any integral numeric value (size limitations apply)
Real: any numeric value (size and accuracy limitations apply)
Number: any integer or real value
String: a sequence of UTF-16 code units
Data: a sequence of bytes
List: a sequence of any values
Array: a mapping from strings to values
any: a value of any type

So where does Point come from ?

I note that the TypeDefinition allows the definition of an alias to a core type but I can not see it being used in the code.

[stam]

Sadly the poor state of LCB documentation is what stopped this from every being more widely used...
Anyone new to LCB and wanting to pick this up cannot do so without practically Herculean efforts, and not everyone has the time to dedicate to this sadly...

[bn]

Hi Simon,

In the code the type Point is used e.g.

Code: Select all

  private variable mCenterPoint as Point

Where is this type documented ?
--
--
So where does Point come from ?

I do not know about Types.

However if you look "Point" up in LCB dictionary its "type" is "operator" and it is a list of 2 items; the first is the x-value, the second the y-value.

Code: Select all

variable tPoint as Point
put point [50, 100] into tPoint

So declaring a variable as "point" sets the format of the variable to a list with 2 items. (Creates a new point value.)
It has as properties

Code: Select all

the x of tPoint
the y of tPoint

I take it as it is used and it is very handy to use this defined variable.
Also it is probably a lot easier to compile since there is a lot less guesswork.

I realise that this does not answer fully your question but this is all I can offer.

Kind regards
Bernd

[Simon Knight]

So it seems that Point defines a special form of List i.e. inherits from List (object?) and overrides index processing?

I find it slightly strange to use an operator in a variable definition. However I see that Path, and Image are used in a similar way i.e.complex variable type definitions. The language reference needs fleshing out.

Perhaps this is what the following quote from the dictionary means

Note: In a subsequent update you will be able to define record types (named collections of values - like structs in C) and handler types (allowing dynamic handler calls through a variable - like function pointers in C).

Hard going for a Xtalk programmer!

[PaulDaMacMan]

So it seems that Point defines a special form of List i.e. inherits from List (object?) and overrides index processing?

I find it slightly strange to use an operator in a variable definition. However I see that Path, and Image are used in a similar way i.e.complex variable type definitions. The language reference needs fleshing out.

Perhaps this is what the following quote from the dictionary means

Note: In a subsequent update you will be able to define record types (named collections of values - like structs in C) and handler types (allowing dynamic handler calls through a variable - like function pointers in C).

Hard going for a Xtalk programmer!

I think the 'point' syntax is probably a type defined in a language module (there's a third type of LCB extension type besides widget and library)
I think it's this one "com.livecode.canvas".
But yes a Point type is basically just an array with two elements, the x,y coordinate numbers.
'Path' type is basically an aliased string type, Image type just an alias of Data byte stream type
Last I checked you don't neccisarly even need to provide an 'as variable-type' it will do some type inference.
I know in the past I've just used stuff like:

Code: Select all

variable tMySVGPathString

instead of 'variable tMySCGPathString as Path' and it compiled fine. Probably not the best practice to do this.
You can also allow a variable to be entirely undefined with 'optional any':

Code: Select all

variable tNotSureWhatType as optional any

The 'optional' means this variable could contain 'nothing' (undefined / null ) and the 'any' means it could store an ObjCId or it could be a unsigned integer we aren't sure what we're going to be pointing in there.

Structs are possible by using Foreign Type definition strings, sort of like the way the Foreign Function binding strings are if you've seen any of that, which is not very intuitive, but it is a way to declare Record / Structs with fields of various value types (Pointer, Unsigned Integer, etc.). There's a chart somewhere, maybe in the "Extending ..." guide.

You can also use type declarations to make 'type aliases, which is handy when you're dealing with a bunch of pointers to various objects in memory. You don't want to mix up your NSWindow with your NSWindowController, ya know? (trying to think of s better example...)

[PaulDaMacMan]

So it seems that Point defines a special form of List i.e. inherits from List (object?) and overrides index processing?

I find it slightly strange to use an operator in a variable definition. However I see that Path, and Image are used in a similar way i.e.complex variable type definitions. The language reference needs fleshing out.

Perhaps this is what the following quote from the dictionary means

Note: In a subsequent update you will be able to define record types (named collections of values - like structs in C) and handler types (allowing dynamic handler calls through a variable - like function pointers in C).

Hard going for a Xtalk programmer!

I think the 'point' syntax is probably a type defined in a language module (there's a third type of LCB extension type besides widget and library)
I think it's this one "com.livecode.canvas".
But yes a Point type is basically just an array with two elements, the x,y coordinate numbers.
'Path' type is basically an aliased string type, 'Image' type just an alias of Data byte stream type
Last I checked you don't necessarily even need to provide an 'as variable-type', compiler will do some type inference.
I know in the past I've just used stuff like:

Code: Select all

variable tMySVGPathString

instead of 'variable tMySCGPathString as Path' and it compiled fine. Probably not the best practice to do this.
You can also allow a variable to be entirely undefined with 'optional any':

Code: Select all

variable tNotSureWhatType as optional any

The 'optional' means this variable could contain 'nothing' (undefined / null ) and the 'any' means it could store an ObjCId or it could be a unsigned integer we aren't sure what we're going to be putting in there.

Structs are possible by using Foreign Type definition strings, sort of like the way the Foreign Function binding strings are if you've seen any of that, which is not very intuitive, but it is a way to declare Record / Structs with fields of various value types (Pointer, Unsigned Integer, etc.). There's a chart somewhere, maybe in the "Extending ..." guide.

You can also use type declarations to make 'type aliases, which is handy when you're dealing with a bunch of pointers to various objects in memory. You don't want to mix up your NSWindow with your NSWindowController, ya know? (trying to think of s better example...)

[PaulDaMacMan]

Sorry for double post, had a Wifi issue.

[PaulDaMacMan]

Yes, that's where these types are defined in that canvas module, they're linked to internal engine stuff with FFI bindings.
The LCB source code for the language module is viewable here:
https://github.com/livecode/livecode/bl ... canvas.lcb.

[Simon Knight]

Thanks Paul,

Given the recent announcement I'm "considering my position" as they say.

[PaulDaMacMan]

Thanks Paul,

Given the recent announcement I'm "considering my position" as they say.

I hear ya, understandable. Well I'll go back to my corner now.