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find a way to pick a default implementation for collection binding

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...through the use of partial specialisation and SFINAE.
There are some rather specific (yet expectedly not uncommon) cases,
where we'd be able to provide a sensible default for the
- match predicate
- new element constructor
of the binding. While in all other cases, the user
has to provide an explicit implementation for these
crucial building blocks anyway.
This commit is contained in:
Fischlurch 2016-03-24 17:32:19 +01:00
parent 4e6fd86c8d
commit 3b116fe6ef
1 changed files with 54 additions and 15 deletions
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69
src/lib/diff/tree-mutator-collection-binding.hpp
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@ -383,6 +383,55 @@
};
using lib::meta::Yes_t;
using lib::meta::No_t;
using lib::meta::enable_if;
template<typename ELM>
struct can_wrap_in_GenNode
{
template<class X>
static Yes_t check(typename lib::variant::CanBuildFrom<X, lib::diff::DataValues>::Type*);
template<class X>
static No_t check(...);
public:
static const bool value = (sizeof(Yes_t)==sizeof(check<ELM>(0)));
};
template<typename ELM, typename SEL =void>
struct _DefaultPayload
{
static bool
match (GenNode const& spec, ELM const& elm)
{
UNIMPLEMENTED("lalü");
}
static ELM
construct (GenNode const& spec)
{
UNIMPLEMENTED("lalü");
}
};
template<typename ELM>
struct _DefaultPayload<ELM, enable_if<can_wrap_in_GenNode<ELM>>>
{
static bool
match (GenNode const& spec, ELM const& elm)
{
return spec.matches(elm);
}
static ELM
construct (GenNode const& spec)
{
return spec.data.get<ELM>();
}
};
/**
* starting point for configuration of a binding to STL container.
* When using the "nested DSL" to setup a binding to child elements
@ -400,17 +449,7 @@
using Coll = typename Strip<COLL>::TypeReferred;
using Elm = typename Coll::value_type;
static bool
default_contentMatch (GenNode const& spec, Elm const& elm)
{
return spec.matches(elm);
}
static Elm
default_construct_from_payload (GenNode const& spec)
{
return spec.data.get<Elm>();
}
using Payload = _DefaultPayload<Elm>;
static bool
disable_selector (GenNode const&)
@ -433,8 +472,8 @@
using FallbackBindingConfiguration
= CollectionBindingBuilder<Coll
,decltype(&default_contentMatch)
,decltype(&default_construct_from_payload)
,decltype(&Payload::match)
,decltype(&Payload::construct)
,decltype(&disable_selector)
,decltype(&disable_assignment)
,decltype(&disable_childMutation)
@ -444,8 +483,8 @@
attachTo (Coll& coll)
{
return FallbackBindingConfiguration{ coll
, default_contentMatch
, default_construct_from_payload
, Payload::match
, Payload::construct
, disable_selector
, disable_assignment
, disable_childMutation