Provide transformations that add member meta-info to common tuple-like constructor calls
Description
Consider the following example (from http://groups.google.com/group/nhusers/browse_thread/thread/7289619c4eceaf2b):
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from u in db.Users
select new KeyValuePair<string, DateTime>(u.Name, u.RegisteredAt) into nameRegistered
order by nameRegistered.ValueThe provider cannot know that u.Name goes into nameRegistered.Value. To allow for that, add a custom transformation that adds the metadata to the ctor call:
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NewExpression (
ctorof (KeyValuePair<TK,TV>(TK,TV)),
new[] { keyExpr, valueExpr },
new[] { memberof (KeyValuePair<TK,TV>.Key), memberof (KeyValuePair<TK,TV>.Value) })Transformations such as the one described above are added a set of classes: KeyValuePairNewExpressionTransformer, and DictionaryEntryTransformer, and TupleNewExpressionTransformer, The transformations, which are enabled by default, add the MemberInfo metadata to NewExpressions for KeyValuePair<TKey, TValue>, DictionaryEntry, and the .NET Tuple types.
To implement such a transformation for custom types, derive from MemberAddingNewExpressionTransformerBase.
For LINQ providers customizing the expression tree preprocessing steps applied by the re-linq front-end, add instances of the transformer classes to the ExpressionTransformationStep.
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