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From: Anatoli Tubman (anatoli_at_[hidden])
Date: 2003-10-01 07:06:43

Hi all:

I need a metaprogramming construct which is essentially a map where both
keys and values are types. I understand a map can be implemented as a list of
pairs, but this is not very efficient (i.e. compilation time would suck).

I need following operations:

1. Comparison for equality. Ideally, equal maps would be represented
   identically (by the same C++ type) but this is not a hard requirement.

2. Singleton. Given a (key, value) pair, create a singleton map.

3. Merge. Given two maps and a function "merge_values", create a merged map.
   If a key is present in only one map, get the value from there, otherwise
   the value is merge_values<value1, value2>::type.

All operations need to be as efficient as possible.

I have a solution where maps are represented by *sorted* list, but this
requires that all values have unique and arbitrary integer keys associated
with them (C++ types themselves are unordered). Though all requirements
are met, this is ugly.

Any ideas?

anatoli at ptc dot com -- opinions are mine

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