Add option to skip forward to the generator interface

2 files changed, 43 insertions, 0 deletions

diff --git a/src/catch2/interfaces/catch_interfaces_generatortracker.cpp b/src/catch2/interfaces/catch_interfaces_generatortracker.cpp
index e9fa5dda..4ac23ddb 100644
--- a/src/catch2/interfaces/catch_interfaces_generatortracker.cpp
+++ b/src/catch2/interfaces/catch_interfaces_generatortracker.cpp
@@ -7,6 +7,8 @@
 // SPDX-License-Identifier: BSL-1.0
 
 #include <catch2/interfaces/catch_interfaces_generatortracker.hpp>
+#include <catch2/generators/catch_generators.hpp>
+
 #include <string>
 
 namespace Catch {
@@ -21,6 +23,31 @@ namespace Catch {
             return ret;
         }
 
+        void GeneratorUntypedBase::skipToNthElementImpl( std::size_t n ) {
+            for ( size_t i = m_currentElementIndex; i < n; ++i ) {
+                bool isValid = next();
+                if ( !isValid ) {
+                    Detail::throw_generator_exception(
+                        "Coud not jump to Nth element: not enough elements" );
+                }
+            }
+        }
+
+        void GeneratorUntypedBase::skipToNthElement( std::size_t n ) {
+            if ( n < m_currentElementIndex ) {
+                Detail::throw_generator_exception(
+                    "Tried to jump generator backwards" );
+            }
+            if ( n == m_currentElementIndex ) { return; }
+
+            skipToNthElementImpl(n);
+            // Fixup tracking after moving the generator forward
+            //  * Ensure that the correct element index is set after skipping
+            //  * Invalidate cache
+            m_currentElementIndex = n;
+            m_stringReprCache.clear();
+        }
+
         StringRef GeneratorUntypedBase::currentElementAsString() const {
             if ( m_stringReprCache.empty() ) {
                 m_stringReprCache = stringifyImpl();
diff --git a/src/catch2/interfaces/catch_interfaces_generatortracker.hpp b/src/catch2/interfaces/catch_interfaces_generatortracker.hpp
index d70cb593..eb3871bc 100644
--- a/src/catch2/interfaces/catch_interfaces_generatortracker.hpp
+++ b/src/catch2/interfaces/catch_interfaces_generatortracker.hpp
@@ -35,6 +35,15 @@ namespace Catch {
             //! Customization point for `currentElementAsString`
             virtual std::string stringifyImpl() const = 0;
 
+            /**
+             * Customization point for skipping to the n-th element
+             *
+             * Defaults to successively calling `countedNext`. If there
+             * are not enough elements to reach the nth one, will throw
+             * an error.
+             */
+            virtual void skipToNthElementImpl( std::size_t n );
+
         public:
             GeneratorUntypedBase() = default;
             // Generation of copy ops is deprecated (and Clang will complain)
@@ -59,6 +68,13 @@ namespace Catch {
             std::size_t currentElementIndex() const { return m_currentElementIndex; }
 
             /**
+             * Moves the generator forward **to** the n-th element
+             *
+             * Cannot move backwards. Can stay in place.
+             */
+            void skipToNthElement( std::size_t n );
+
+            /**
              * Returns generator's current element as user-friendly string.
              *
              * By default returns string equivalent to calling