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diff --git a/source/core/slang-string-slice-index-map.h b/source/core/slang-string-slice-index-map.h
new file mode 100644
index 000000000..5aef62253
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+++ b/source/core/slang-string-slice-index-map.h
@@ -0,0 +1,78 @@
+#ifndef SLANG_CORE_STRING_SLICE_INDEX_MAP_H
+#define SLANG_CORE_STRING_SLICE_INDEX_MAP_H
+
+#include "slang-basic.h"
+
+#include "slang-string-slice-pool.h"
+
+namespace Slang
+{
+
+/* Maps an UnownedStringSlice to an index. All substrings are held internally in a StringSlicePool, and so
+owned by the type. 
+*/
+class StringSliceIndexMap
+{
+public:
+        /// An index that identifies a key value pair. 
+    typedef Index CountIndex;
+
+        /// Adds a key, value pair. Returns the CountIndex of the pair.
+        /// If there is already a value stored for the key it is replaced.
+    CountIndex add(const UnownedStringSlice& key, Index valueIndex);
+
+        /// Finds or adds the slice. If the slice is added the defaultValueIndex is set.
+        /// If not the index associated with the slice remains the same.
+        /// Returns the CountIndex where the key,value pair are stored
+    CountIndex findOrAdd(const UnownedStringSlice& key, Index defaultValueIndex);
+
+        /// Gets the index associated with the key. Returns -1 if there is no associated index.
+    SLANG_FORCE_INLINE Index getValue(const UnownedStringSlice& key);
+
+        /// Get the amount of pairs in the map
+    Index getCount() const { return m_indexMap.getCount(); }
+
+        /// Get the slice and the index at the specified index
+    SLANG_INLINE KeyValuePair<UnownedStringSlice, Index> getAt(CountIndex countIndex) const;
+    
+        /// Clear the contents of the map
+    void clear();
+
+        /// Get the key at the specified index
+    UnownedStringSlice getKeyAt(CountIndex index) const { return m_pool.getSlice(StringSlicePool::Handle(index)); }
+        /// Get the value at the specified index
+    Index& getValueAt(CountIndex index) { return m_indexMap[index]; }
+
+        /// Get the amount of key,value pairs
+    Index getCount() { return m_indexMap.getCount(); }
+
+        /// Ctor
+    StringSliceIndexMap() :
+        m_pool(StringSlicePool::Style::Empty)
+    {
+    }
+
+protected:
+    StringSlicePool m_pool;     ///< Pool holds the substrings
+    List<Index> m_indexMap;     ///< Maps a pool index to the output index
+};
+
+// ---------------------------------------------------------------------------
+Index StringSliceIndexMap::getValue(const UnownedStringSlice& key)
+{
+    const Index poolIndex = m_pool.findIndex(key);
+    return (poolIndex >= 0) ? m_indexMap[poolIndex] : -1;
+}
+
+// ---------------------------------------------------------------------------
+KeyValuePair<UnownedStringSlice, Index> StringSliceIndexMap::getAt(CountIndex countIndex) const
+{
+    KeyValuePair<UnownedStringSlice, Index> pair;
+    pair.Key = m_pool.getSlice(StringSlicePool::Handle(countIndex));
+    pair.Value = m_indexMap[countIndex];
+    return pair;
+}
+
+}
+
+#endif