1  #+TITLE: Story 11 - Objects and Operations, revisited
 2  #+OPTIONS: author:nil date:nil
 3  
 4  In [[file:story-7-Objects-and-Operations.org][Story 7 - Objects and Operations]], Data Object constructors (*Import*,
 5  *Generate*, *Load*) are presented as Data Object functions with parameter
 6  sets.
 7  
 8  However, with the revocation of the overly complex ideas on parameter sets,
 9  this also needs some rethinking.
10  
11  * A word on parameters and parameter sets
12  
13  Parameter sets were supposed to be a set of typed data that the Le'Sec
14  libraries would have no knowledge about, and would leave it completely to
15  the application to know what to pass, and to individual implementations
16  (dispatches) to handle.
17  
18  That idea still applies, but the design was over-reaching, and consequently
19  bulky, and needed to be simplified in its core.
20  
21  Experiments showed that it was much simpler to have implementations that
22  need it implement two functions, one to get a parameter value and one to set
23  it, with the parameter selected with a simple number.  The caller /must/
24  know the exact form that this value takes.
25  
26  Exactly how the caller would find out this exact form is subject for
27  [[file:story-12-Parameters.org::+TITLE: Story 12 - Parameters][another story]].
28  
29  * A word on parameters in the context of Objects and of Operations
30  
31  A distinction between Objects and Operations could be made that Objects to
32  not have general parameters, while Operations do.
33  
34  That doesn't mean that Objects can't provide data at all, but it essentially
35  means that data it can provide is determined by the Object Class that it
36  implements rather than by the implementation.  Object parameters revolve
37  more around the payload of the Object, while Operation parameters revolve
38  more around the functionality of that Operation.
39  
40  * Changes in Object functionality
41  
42  The Object functionality in [[file:story-7-Objects-and-Operations.org][Story 7 - Objects and Operations]] is quite
43  complex, too complex even.  Experimentation showed that the idea of pieces
44  and selections was big source of confusion, so things were changed a bit.
45  
46  It was determined that for the /basic/ functionality needs, the following
47  functionality would cover most of it:
48  
49  - Generate ::
50  
51    This generates an Object payload, hopefully randomly, given hints that the
52    functionality would receive in parameter form.
53  
54  - Construct ::
55  
56    This constructs an Object payload from payload data received in parameter
57    form.
58  
59  - Extract ::
60  
61    This extracts Object payload data in parameter form.
62  
63  But this is not enough...
64  
65  * Viewing some Object functionality as Operations
66  
67  The Data Object constructor functionality as well as the extractor can be
68  seen as Operations performed with the associated Object, but by nature, they
69  are especially tightly tied to the associated Object.
70  
71  A solution for this is to move away from the constructor and extractor
72  functionality being provided directly by the Data Object, and move to have
73  the Data Object provide the following functionality instead:
74  
75  - *Get Generator*
76  - *Get Constructor*
77  - *Get Extractor*
78  
79  All of these would do the same thing, to return an ephemeral Operation
80  instance, with which all sorts of things can be done, including dealing with
81  parameters and whatever the implementation allows, and finally call a per
82  Operation specific function to finalize whatever it does.
83  
84  The responsibility to keep track of these ephemeral Operations would remain
85  with the associated Object, so as to not place undue burden on the
86  application.
87  
88  In terms of a Data Object type factory, each of these operation types can be
89  implemented incrementally, as an extension to the base Object factory, or
90  any specialised Object type.
91  
92  ** What happened with the other Object functionality?
93  
94  *Import*, *Export* and *Load* are now deferred, they have been deemed
95  unnecessary at this stage.  They are not lost, though, they will just be
96  picked up later.