🚀 go-pugleaf

hi,
i'm trying to save data (long string with unknown size) to a file.
i need help - i tried to read the posts here about the subject, but i
still don't know what to do.

what i want to do - 
save a record to a file , the record has strings (with known size) &
strings (with UNKNOWN size) & integers.
i tried to declared the unknown sized string as "array of char" or
"string" or "^ ArrayOfCharType", but each time i got in the saved file
a pointer to this vaiable, and i want the data of it.

i had to declared the file variable as "file" and not as "file of
EntryType" due to the problem of finalization.

here is an example : 

type
     EntryType = record
       str1 : string[255];
       str2 : string[255];
       Num1 : integer;
       largeStr : array of char;
    end;  

procedure ...
var
   MyFile : file;
   MyRec : EntryType ;
   sourceStr : string; // a large string that i have from some other
place with unknown size (until i get it)
begin
        sourceStr := getSourceString();
        SetLength(MyRec.largeStr, length(sourceStr));

        // the next line also give me an error, thats why i did a loop
        // MyRec.largeStr := sourceStr;

        for i := 1 to length(sourceStr) do
            begin
                    MyRec.largeStr[i-1] := Char(sourceStr[i]);
            end;

        MyRec.str1 := 'line1';
        MyRec.str2 := 'line2';     
        MyRec.num1 := 123record;
        
        AssignFile(MyFile,'data1.dat');
        rewrite(MyFile,1);
        BlockWrite(MyFile, MyRec, sizeof(MyRec));
        closeFile(MyFile);
end;

thanks,
Shay