Use C++17 fold expressions when casting tuples and argument lists
This commit introduces the use of C++17-style fold expressions when
casting tuples & the argument lists of functions.
This change can improve performance of the resulting bindings: because
fold expressions have short-circuiting semantics, pybind11 e.g. won't
try to cast the second argument of a function if the first one failed.
This is particularly effective when working with functions that have
many overloads with long argument lists.
diff --git a/include/pybind11/cast.h b/include/pybind11/cast.h
index 3af6735..38eb8a8 100644
--- a/include/pybind11/cast.h
+++ b/include/pybind11/cast.h
@@ -1432,9 +1432,14 @@
template <size_t... Is>
bool load_impl(const sequence &seq, bool convert, index_sequence<Is...>) {
+#ifdef __cpp_fold_expressions
+ if ((... || !std::get<Is>(subcasters).load(seq[Is], convert)))
+ return false;
+#else
for (bool r : {std::get<Is>(subcasters).load(seq[Is], convert)...})
if (!r)
return false;
+#endif
return true;
}
@@ -1961,9 +1966,14 @@
template <size_t... Is>
bool load_impl_sequence(function_call &call, index_sequence<Is...>) {
+#ifdef __cpp_fold_expressions
+ if ((... || !std::get<Is>(argcasters).load(call.args[Is], call.args_convert[Is])))
+ return false;
+#else
for (bool r : {std::get<Is>(argcasters).load(call.args[Is], call.args_convert[Is])...})
if (!r)
return false;
+#endif
return true;
}
