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[Markos Zaharioudakis <markos_za@xxxxxxxxx>]

Here are a few problems I can see so far:

1. I don't think we can do function caching for variadic functions. The current implementation of user_function::computeResultCaching certainly does not support variadic functions, but more importantly, we need a fixed number of params to form the index key (unless we start thinking towards having more than one cache for variadic functions).

2. The user_function::computeResultCaching does the full computation every time it is invoked (and it may be invoked multiple times from the codegen). It should cache the result of the 1st computation and simply return it afterwards.

3. In UDFunctionCallIterator::createCache, the line:
   lSpec.theKeyTypes[i] = sig[i]->get_qname().getp();
is not correct if the type of the param is a user-defined type (because the store will not understand its name). You must call getBaseBuiltinType() of the param type first (like the translator does in line 4401).

4. It's probably worthwhile to do something so that we don't have to recompute the args in case of a cache miss. What we have to do is create a temp sequence for each arg, and fill it with the corresponding arg value; then bind the arg reference to that temp seq, instead the arg wrapper.

5. It's probably worthwhile to allow subtypes of xs:anyAtomicType? as param types. Index creation already supports "null" keys, but we will need a new probe function. This we should probably do as a phase-2 task.
-- 
https://code.launchpad.net/~matthias-brantner/zorba/caching/+merge/81304
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