6 files changed, 547 insertions, 9 deletions
diff --git a/source/core/slang-castable-list-impl.cpp b/source/core/slang-castable-list-impl.cpp
new file mode 100644
index 000000000..ee10ea995
--- /dev/null
+++ b/source/core/slang-castable-list-impl.cpp
@@ -0,0 +1,178 @@
+// slang-castable-list-impl.cpp
+#include "slang-castable-list-impl.h"
+
+namespace Slang {
+
+    /* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! UnknownCastableAdapter !!!!!!!!!!!!!!!!!!!!!!!!!!! */
+
+void* UnknownCastableAdapter::castAs(const Guid& guid)
+{
+    if (auto intf = getInterface(guid))
+    {
+        return intf;
+    }
+    if (auto obj = getObject(guid))
+    {
+        return obj;
+    }
+
+    if (m_found && guid == m_foundGuid)
+    {
+        return m_found;
+    }
+
+    ComPtr<ISlangUnknown> cast;
+    if (SLANG_SUCCEEDED(m_contained->queryInterface(guid, (void**)cast.writeRef())) && cast)
+    {
+        // Save the interface in the cache
+        m_found = cast;
+        m_foundGuid = guid;
+
+        return cast;
+    }
+    return nullptr;
+}
+
+void* UnknownCastableAdapter::getInterface(const Guid& guid)
+{
+    if (guid == ISlangUnknown::getTypeGuid() ||
+        guid == ICastable::getTypeGuid())
+    {
+        return static_cast<ICastable*>(this);
+    }
+    return nullptr;
+}
+
+void* UnknownCastableAdapter::getObject(const Guid& guid)
+{
+    SLANG_UNUSED(guid);
+    return nullptr;
+}
+
+/* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! CastableList !!!!!!!!!!!!!!!!!!!!!!!!!!! */
+
+CastableList::~CastableList()
+{
+    for (auto castable : m_list)
+    {
+        castable->release();
+    }
+}
+
+void* CastableList::castAs(const Guid& guid)
+{
+    if (auto intf = getInterface(guid))
+    {
+        return intf;
+    }
+    return getObject(guid);
+}
+
+void* CastableList::getInterface(const Guid& guid)
+{
+    if (guid == ISlangUnknown::getTypeGuid() ||
+        guid == ICastable::getTypeGuid() ||
+        guid == ICastableList::getTypeGuid())
+    {
+        return static_cast<ICastableList*>(this);
+    }
+    return nullptr;
+}
+
+void* CastableList::getObject(const Guid& guid)
+{
+    SLANG_UNUSED(guid);
+    return nullptr;
+}
+
+void* CastableList::find(const Guid& guid)
+{
+    for (ICastable* castable : m_list)
+    {
+        if (auto ptr = castable->castAs(guid))
+        {
+            return ptr;
+        }
+    }
+    return nullptr;
+}
+
+Index CastableList::indexOf(ICastable* castable)
+{
+    const Count count = m_list.getCount();
+    for (Index i = 0; i < count; ++i)
+    {
+        ICastable* cur = m_list[i];
+        if (cur == castable)
+        {
+            return i;
+        }
+    }
+    return -1;
+}
+
+void CastableList::add(ICastable* castable) 
+{ 
+    SLANG_ASSERT(castable);
+    castable->addRef();
+    m_list.add(castable);
+}
+
+void CastableList::removeAt(Index i) 
+{ 
+    auto castable = m_list[i];
+    m_list.removeAt(i);
+    castable->release();
+}
+
+void CastableList::clear() 
+{ 
+    for (auto castable : m_list)
+    {
+        castable->release();
+    }
+    m_list.clear(); 
+}
+
+void CastableList::addUnknown(ISlangUnknown* unk)
+{
+    // If it has ICastable interface we can just add as that
+    {
+        ComPtr<ICastable> castable;
+        if (SLANG_SUCCEEDED(unk->queryInterface(ICastable::getTypeGuid(), (void**)castable.writeRef())) && castable)
+        {
+            return add(castable);
+        }
+    }
+
+    // Wrap it in an adapter
+    IUnknownCastableAdapter* adapter = new UnknownCastableAdapter(unk);
+    add(adapter);
+}
+
+Index CastableList::indexOfUnknown(ISlangUnknown* unk)
+{
+    SLANG_ASSERT(unk);
+    // If it has a castable interface we can just look for that
+    {
+        ComPtr<ICastable> castable;
+        if (SLANG_SUCCEEDED(unk->queryInterface(ICastable::getTypeGuid(), (void**)castable.writeRef())) && castable)
+        {
+            return indexOf(castable);
+        }
+    }
+
+    // It's not derived from ICastable, so can only be in list via an adapter
+    const Count count = m_list.getCount();
+    for (Index i = 0; i < count; ++i)
+    {
+        auto adapter = as<IUnknownCastableAdapter>(m_list[i]);
+        if (adapter && adapter->getContained() == unk)
+        {
+            return i;
+        }
+    }
+    return -1;
+}
+
+} // namespace Slang
diff --git a/source/core/slang-castable-list-impl.h b/source/core/slang-castable-list-impl.h
new file mode 100644
index 000000000..6c03855f2
--- /dev/null
+++ b/source/core/slang-castable-list-impl.h
@@ -0,0 +1,83 @@
+// slang-castable-list.h
+#ifndef SLANG_CASTABLE_LIST_IMPL_H
+#define SLANG_CASTABLE_LIST_IMPL_H
+
+#include "slang-castable-list.h"
+
+#include "../../slang-com-helper.h"
+#include "../../slang-com-ptr.h"
+
+#include "../core/slang-com-object.h"
+
+namespace Slang
+{
+
+/* An adapter such that types which aren't derived from ICastable, can be used as such. 
+
+With the following caveats.
+* the interfaces/objects of the adapter are checked *first*, so IUnknown will always be for the adapter
+* assumes when doing a queryInterface on the contained item, it will remain in scope when released (this is *not* strict COM)
+*/
+class UnknownCastableAdapter : public ComBaseObject, public IUnknownCastableAdapter
+{
+public:
+    SLANG_COM_BASE_IUNKNOWN_ALL
+
+    // ICastable
+    SLANG_NO_THROW void* SLANG_MCALL castAs(const Guid& guid) SLANG_OVERRIDE;
+
+    // IUnknownCastableAdapter
+    virtual SLANG_NO_THROW ISlangUnknown* SLANG_MCALL getContained() SLANG_OVERRIDE { return m_contained; }
+
+    UnknownCastableAdapter(ISlangUnknown* unk):
+        m_contained(unk)
+    {
+        SLANG_ASSERT(unk);
+    }
+
+protected:
+    void* getInterface(const Guid& guid);
+    void* getObject(const Guid& guid);
+
+    ComPtr<ISlangUnknown> m_contained;
+
+    // We hold a cache for a single lookup to make things a little faster
+    void* m_found = nullptr;
+    Guid m_foundGuid;
+};
+
+/* Implementation of the ICastableList interface. 
+Is atomic reference counted*/
+class CastableList : public ComBaseObject, public ICastableList
+{
+public:
+    SLANG_COM_BASE_IUNKNOWN_ALL
+
+    // ICastable
+    SLANG_NO_THROW void* SLANG_MCALL castAs(const Guid& guid) SLANG_OVERRIDE;
+
+    // ICastableList
+    virtual Count SLANG_MCALL getCount() SLANG_OVERRIDE { return m_list.getCount(); }
+    virtual ICastable* SLANG_MCALL getAt(Index i) SLANG_OVERRIDE { return m_list[i]; }
+    virtual void SLANG_MCALL add(ICastable* castable) SLANG_OVERRIDE;
+    virtual void SLANG_MCALL addUnknown(ISlangUnknown* unk) SLANG_OVERRIDE;
+    virtual void SLANG_MCALL removeAt(Index i) SLANG_OVERRIDE;
+    virtual void SLANG_MCALL clear() SLANG_OVERRIDE;
+    virtual Index SLANG_MCALL indexOf(ICastable* castable) SLANG_OVERRIDE;
+    virtual Index SLANG_MCALL indexOfUnknown(ISlangUnknown* unk) SLANG_OVERRIDE;
+    virtual void* SLANG_MCALL find(const Guid& guid) SLANG_OVERRIDE;
+    virtual ICastable*const* SLANG_MCALL getBuffer() SLANG_OVERRIDE { return m_list.getBuffer(); }
+
+        /// Dtor
+    virtual ~CastableList();
+
+protected:
+    void* getInterface(const Guid& guid);
+    void* getObject(const Guid& guid);
+
+    List<ICastable*> m_list;
+};
+
+} // namespace Slang
+
+#endif
diff --git a/source/core/slang-castable-list.h b/source/core/slang-castable-list.h
new file mode 100644
index 000000000..942f53376
--- /dev/null
+++ b/source/core/slang-castable-list.h
@@ -0,0 +1,57 @@
+// slang-castable-list.h
+#ifndef SLANG_CASTABLE_LIST_H
+#define SLANG_CASTABLE_LIST_H
+
+#include "../core/slang-basic.h"
+
+#include "../core/slang-destroyable.h"
+
+namespace Slang
+{
+
+/* A useful interface for handling lists of castable interfaces. Cannot hold nullptr */
+class ICastableList : public ICastable
+{
+    SLANG_COM_INTERFACE(0x335f3d40, 0x934c, 0x40dc, { 0xb5, 0xe1, 0xf7, 0x6e, 0x40, 0x3, 0x62, 0x5 })
+            
+        /// Get the count of all interfaces held in the list
+    virtual Count SLANG_MCALL getCount() = 0;
+        /// Get the interface at the specified index
+    virtual ICastable* SLANG_MCALL getAt(Index i) = 0;
+        /// Add an item to the list
+    virtual void SLANG_MCALL add(ICastable* unk) = 0;
+        /// Add IUnknown, will cast to ICastable and if that's not possible will wrap
+    virtual void SLANG_MCALL addUnknown(ISlangUnknown* unk) = 0;
+        /// Remove item at index, remaining items stay in the same order
+    virtual void SLANG_MCALL removeAt(Index i) = 0;
+        /// Clear the list
+    virtual void SLANG_MCALL clear() = 0;
+        /// Find the first index of castable, or -1 if not found
+    virtual Index SLANG_MCALL indexOf(ICastable* castable) = 0;
+        /// Find the index interface (handling wrapping if necessary)
+    virtual Index SLANG_MCALL indexOfUnknown(ISlangUnknown* unk) = 0;
+        /// Find the first item that casts to non null
+    virtual void* SLANG_MCALL find(const Guid& guid) = 0;
+        /// Access the internal buffer (any mutation can invalidate this value)
+    virtual ICastable*const* SLANG_MCALL getBuffer() = 0;
+};
+
+// Simply finding things in a ICastableList
+template <typename T>
+SLANG_FORCE_INLINE T* find(ICastableList* list)
+{
+    return reinterpret_cast<T*>(list->find(T::getTypeGuid())); 
+}
+
+/* Adapter interface to make a non castable types work as ICastable */
+class IUnknownCastableAdapter : public ICastable
+{
+    SLANG_COM_INTERFACE(0x8b4aad81, 0x4934, 0x4a67, { 0xb2, 0xe2, 0xe9, 0x17, 0xfc, 0x29, 0x12, 0x54 });
+
+    /// When using the adapter, this provides a way to directly get the internal no ICastable type
+    virtual SLANG_NO_THROW ISlangUnknown* SLANG_MCALL getContained() = 0;
+};
+
+} // namespace Slang
+
+#endif
diff --git a/source/core/slang-destroyable.h b/source/core/slang-destroyable.h
index bf373ba33..390b16e7c 100644
--- a/source/core/slang-destroyable.h
+++ b/source/core/slang-destroyable.h
@@ -9,15 +9,6 @@
 namespace Slang
 {
 
-/* Adapter interface to make a non castable type work as ICastable */
-class IUnknownCastableAdapter : public ICastable
-{
-    SLANG_COM_INTERFACE(0x8b4aad81, 0x4934, 0x4a67, { 0xb2, 0xe2, 0xe9, 0x17, 0xfc, 0x29, 0x12, 0x54 } );
-
-        /// When using the adapter, this provides a way to directly get the internal no ICastable type
-    virtual SLANG_NO_THROW ISlangUnknown* SLANG_MCALL getContained() = 0;
-};
-
 /* An interface that allows for an object to implement 'destruction'. A destroyed 
 interface/object should release any other contained references. 
 Behavior of an interface that is IDestroyed should be defined on the interface. Typically 
diff --git a/source/core/slang-lazy-castable-list.cpp b/source/core/slang-lazy-castable-list.cpp
new file mode 100644
index 000000000..d9f0090d5
--- /dev/null
+++ b/source/core/slang-lazy-castable-list.cpp
@@ -0,0 +1,163 @@
+// slang-lazy-castable-list.cpp
+#include "slang-lazy-castable-list.h"
+
+#include "slang-castable-list-impl.h"
+
+namespace Slang {
+
+void LazyCastableList::removeAt(Index index)
+{
+    SLANG_ASSERT(index >= 0 && index < getCount());
+
+    switch (m_state)
+    {
+        case State::None:   break;
+        case State::One:    
+        {
+            m_state = State::None;
+            m_castable.setNull();
+            break;
+        }
+        case State::List:   
+        {
+            static_cast<ICastableList*>(m_castable.get())->removeAt(index);
+            break;
+        }
+    }
+}
+
+void LazyCastableList::clear()
+{
+    if (m_state == State::List)
+    {
+        auto list = static_cast<ICastableList*>(m_castable.get());
+        list->clear();
+    }
+    else
+    {
+        m_state = State::None;
+        m_castable.setNull();
+    }
+}
+
+void LazyCastableList::clearAndDeallocate()
+{
+    m_state = State::None;
+    m_castable.setNull();
+}
+
+Count LazyCastableList::getCount() const
+{
+    switch (m_state)
+    {
+        case State::None:   return 0;
+        case State::One:    return 1;
+        default:
+        case State::List:   return static_cast<ICastableList*>(m_castable.get())->getCount();
+    }
+}
+
+void LazyCastableList::add(ICastable* castable)
+{
+    SLANG_ASSERT(castable);
+    if (m_state == State::None)
+    {
+        m_castable = castable;
+        m_state = State::One;
+    }
+    else
+    {
+        requireList()->add(castable);
+    }
+}
+
+ICastableList* LazyCastableList::requireList()
+{
+    switch (m_state)
+    {
+        case State::None:
+        {
+            m_castable = new CastableList;
+            m_state = State::List;
+            break;
+        }
+        case State::One:
+        {
+            // Turn into a list
+            auto list = new CastableList;
+            list->add(m_castable);
+            m_castable = list;
+            m_state = State::List;
+            break;
+        }
+        default: break;
+    }
+    SLANG_ASSERT(m_state == State::List);
+    return static_cast<ICastableList*>(m_castable.get());
+}
+
+ICastableList* LazyCastableList::getList()
+{
+    return (m_state == State::None) ? nullptr : requireList();
+}
+
+void* LazyCastableList::find(const Guid& guid)
+{
+    for (auto castable : getView())
+    {
+        if (auto ptr = castable->castAs(guid))
+        {
+            return ptr;
+        }
+    }
+    return nullptr;
+}
+ 
+ConstArrayView<ICastable*> LazyCastableList::getView() const
+{
+    switch (m_state)
+    {
+        case State::None: return ConstArrayView<ICastable*>();
+        case State::One:  return ConstArrayView<ICastable*>((ICastable*const*)&m_castable, 1);
+        default:
+        case State::List:
+        {
+            auto list = static_cast<ICastableList*>(m_castable.get());
+            return ConstArrayView<ICastable*>(list->getBuffer(), list->getCount());
+        }
+    }
+}
+
+Index LazyCastableList::indexOf(ICastable* castable) const
+{
+    return getView().indexOf(castable);
+}
+
+Index LazyCastableList::indexOfUnknown(ISlangUnknown* unk) const
+{
+    // Try as a ICastable first
+    {
+        ComPtr<ICastable> castable;
+        if (SLANG_SUCCEEDED(unk->queryInterface(ICastable::getTypeGuid(), (void**)castable.writeRef())) && castable)
+        {
+            return indexOf(castable);
+        }
+    }
+
+    // It's not derived from ICastable, so can only be in list via an adapter
+    const auto view = getView();
+
+    const Count count = view.getCount();
+    for (Index i = 0; i < count; ++i)
+    {
+        auto adapter = as<IUnknownCastableAdapter>(view[i]);
+        if (adapter && adapter->getContained() == unk)
+        {
+            return i;
+        }
+    }
+
+    return -1;
+}
+
+} // namespace Slang
diff --git a/source/core/slang-lazy-castable-list.h b/source/core/slang-lazy-castable-list.h
new file mode 100644
index 000000000..4f73ce9ca
--- /dev/null
+++ b/source/core/slang-lazy-castable-list.h
@@ -0,0 +1,66 @@
+// slang-lazy-castable-list.h
+#ifndef SLANG_LAZY_CASTABLE_LIST_H
+#define SLANG_LAZY_CASTABLE_LIST_H
+
+#include "slang-castable-list.h"
+
+#include "../../slang-com-ptr.h"
+
+namespace Slang
+{
+
+/* Sometimes the overhead around having a potential list of items that might often be 
+empty or only contain a single element is considerable. 
+
+The `LazyCastableList` provides functionality around ICastableList to minimize allocation, or the 
+need to allocate an ICastableList. It does this by tracking state in m_state, and varying the 
+meaning of m_castable. 
+
+* State::None - there is no list 
+* State::One - there is a single entry, that is held in m_castable
+* State::List - m_castable is actually ICastableList, and holds the contents
+*/
+class LazyCastableList
+{
+public:
+        /// Add a castable to the lsit
+    void add(ICastable* castable);
+        /// Return the amount of items in the list
+    Count getCount() const;
+        /// Remove the item at the specified index
+    void removeAt(Index index);
+        /// Clear the list
+    void clear();
+        /// Clear and deallocate the list
+    void clearAndDeallocate();
+        /// Find the first item that castAs(guid) produces a result
+    void* find(const Guid& guid);
+        /// Get the contents of the list as a view
+    ConstArrayView<ICastable*> getView() const;
+        /// Get the index of castable in the list. Returns -1 if not found
+    Index indexOf(ICastable* castable) const;
+        /// Get the index of unk. Handles if the wrapping has been used.
+    Index indexOfUnknown(ISlangUnknown* unk) const;
+
+        /// Will always return a valid ICastableList
+    ICastableList* requireList();
+        /// Will return nullptr if the list is empty, else it returns a ICastableList holding the elements
+    ICastableList* getList();
+
+protected:
+    enum class State
+    {
+        None,
+        One,
+        List,
+    };
+    // A state is not *strictly* necessary, because we can always determine what m_castable is
+    // with a castAs. But doing so is not exactly fast, and using the state makes some code simpler
+    // additionally.
+    State m_state = State::None;
+    ComPtr<ICastable> m_castable;
+};
+
+} // namespace Slang
+
+#endif