Returning complex types from AL functions.
Jalmaraz
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ReportI notice that AL lets us to return some complex types in functions. This function bellow saves recordref content in a Json object and returns it:
procedure GetJSonFromGeneric(var GenericRec: RecordRef) JsonGeneric: JsonObject
var
i: Integer;
GenericField: FieldRef;
begin
for i := 1 to GenericRec.FieldCount() do begin
GenericField := GenericRec.FieldIndex(i);
JsonGeneric.Add(GenericField.Name,
format(GenericField.Value));
end;
end;
The amazing stuff begins when we consume this function:
trigger OnRun()
var
Customer: record Customer;
GenericRec: RecordRef;
BodyText: Text;
begin
Customer.FindFirst();
GenericRec.GetTable(Customer);
GetJSonFromGeneric(GenericRec).WriteTo(BodyText);
message(BodyText);
end;
The function became an object itself with all methods and properties of Json object!!!
The subtle difference. Code highlights.
First, we declare the function with a complex type return:
procedure GetJSonFromGeneric(var GenericRec: RecordRef) JsonGeneric: JsonObject
Later we consume this function, handling it as an object:
GetJSonFromGeneric(GenericRec).WriteTo(BodyText);
To do the same in old C/AL we must send a parameter with “Var” mark, and then can save changes in this parameter:
procedure GetJSonFromGenericWithPar(var GenericRec: RecordRef;var JsonGeneric: JsonObject)
You may think “who cares?”.
But it´s more important than you might think. I can give you two reasons:
- Input/output parameters (marked with “var”) are generally avoided in all programming paradigms, functional and OOP as well. Modifying a parameter instead returning a new object could cause many errors hard to fix. Parameters by reference can get some state behind that turns code unsafe.
- All the signs are that we are going to get new features in AL functions, comparable to JavaScript functions. The future could get us callbacks or the possibility of returns a record.
Objects that can be returned.
Not all the objects are valid return types. My strongest desire is return a record, the absolute king of Dynamics objects. But not possible:
But despite this, there are a lot of interesting objects to return:
local procedure MyProcedure1(): XmlDocument
begin
end;
local procedure MyProcedure2(): HttpHeaders
begin
end;
I preferred to use Jason Object in the example because is another very important object: a JavaScript complete object definition.
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