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introduce special treatment for RecRef payload

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The intention is to allow a Ref to "stand-in" for
a GenNode holding a full Record inline
This commit is contained in:
Fischlurch 2015-09-17 19:00:55 +02:00
parent 7f2e328ab3
commit 269ef07655
1 changed files with 60 additions and 3 deletions
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63
src/lib/diff/gen-node.hpp
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@ -188,6 +188,11 @@ namespace diff{
Locator expand() const;
operator string() const;
template<typename X>
X& get();
template<typename X>
X const& get() const;
};
@ -345,7 +350,7 @@ namespace diff{
/* === iteration / recursive expansion / references === */
/* === iteration / recursive expansion === */
/**
@ -495,6 +500,58 @@ namespace diff{
/* === References : special treatment on element access === */
template<typename X>
inline X&
DataCap::get()
{
return Variant<DataValues>::get<X>();
}
template<typename X>
inline X const&
DataCap::get() const
{
return Variant<DataValues>::get<X>();
}
/** especially when accessing for a Record,
* a payload of type \c RecordRef<Record<GenNode>> (aka RecRef)
* will be automatically dereferenced. Effectively this allows
* a GenNode with a RecRef payload to "stand in" for a node holding
* a full Record inline. And it allows the construction of a special
* \link #Ref Ref-GenNode \endlink, which even shares the \em identity
* (the ID) of the referenced record-GenNode.
* @note effectively this opens an indirect loophole to const correctness,
* since it is possible explicitly to retrieve the RecRef from a
* const GenNode and then to access the referred-to Record
* without const. In case this turns out to be problematic,
* we'd have to alter the semantics of RecRef
*/
template<>
inline Rec&
DataCap::get()
{
Rec* rec = maybeGet<Rec>();
if (rec) return *rec;
return Variant<DataValues>::get<RecRef>();
}
template<>
inline Rec const&
DataCap::get() const
{
Rec* rec = unConst(this)->maybeGet<Rec>();
if (rec) return *rec;
return Variant<DataValues>::get<RecRef>();
}
/**
* Constructor for a specially crafted 'ref GenNode'.
* The identity record of the generated object will be prepared
@ -509,8 +566,8 @@ namespace diff{
*/
explicit
Ref(string const& symbolicID)
: GenNode(fabricateRefID<RecRef> (symbolicID)
, DataCap(RecRef())) // note: places NIL into the reference part
: GenNode(fabricateRefID<Rec> (symbolicID)//note: seeds the type hash with Rec, not RecRef
, DataCap(RecRef())) // note: places NIL into the reference part
{ }
/** build reference to a Record, using the original ID