[fpc-pascal] flexible record design

[spir ☣]

Hello,

I'm looking for a "convenient" way to implement a type for kinds of flexible records. "Best" means simple and efficient. A flexible record is a kind of set of name:value symbol, but completely modifyable at runtime. The necessary untyped aspect of the question is handled by values beeing pointers.
Compared to a mapping *collection*, these objects have some specificity:
* conceptually, each one forms a single, whole, data unit -- as opposed to a set of data.
* Keys are all names (thus, a subset of string), and rather short.
* The number of symbols is typically small; these object are defined by hand! As opposed to extremely varying & possibly huge numbers of collection items.

The most important operation for such an object is value lookup. Some trials have shown me that data structures with sophisticated algorithms such as radix tries or hash table are counter productive (they are severely outperformed by simple sequences up to > 100 items). --> http://groups.google.com/group/pilud/browse_thread/thread/9d7992f97c976cef#



The simplest method may be to create a tool type for name:value symbols, and put this into a TFPList. Lookup is thus traversing the sequence, checking the name until found, returning the value.

Another way would be to hold // sequences for names and values. Lookup should be faster, since names are not hidden in symbol structure. Once a name's index is known, the matching value can be reached using this index. I guess the name sequence could be at best a linked list, since it's only traversed; while values, which are only indexed, should be held in a flexible array (TFPList) for direct indexing. Comments?



But I'm a bit troubled by the documentation about TStrings. TStrings declares interface methods to deal with "associated objects" (not implemented) and "value parts", eg:
   function AddObject(); virtual;   Add a string and associated object to the list.
   property ValueFromIndex: String; [rw]   Return the value part of a string based on it's index.
The description of the type reads:
"...  It also allows an arbitrary object to be associated with each string.
It also introduces methods to manage a series of name=value settings, as found in many configuration files..."

Side-question: What is the purpose of introducing unimplemented methods? Sub-classes can extend a super-class anyway, no? Is it just an incentive to implement those methods?

I would like to know the underlying structure of TString (linked list, "flexible-ised" dynamic array, what else?).
What is actually a name:value association? How does it work and how is one supposed to use it? The _name_ of the feature perfectly fits my needs :-) but can I use it for my flexible record type?
Associated objects are not implemented at all (all methods virtual). How is one supposed to design such a feature? Associate a // list of objects (maintaining matching indexes)? But if a TString is an array, lookup is probably slower than necessary (since it's a plain traversal), or am I wrong on this?

Thank you for your patience with a newcomer :-)


Denis
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vit esse estrany ☣

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