compat: add map/filter template functions

1 files changed, 75 insertions, 0 deletions

diff --git a/compat/functional.hpp b/compat/functional.hpp
new file mode 100644
index 00000000..e7229d6e
--- /dev/null
+++ b/compat/functional.hpp
@@ -0,0 +1,75 @@
+#pragma once
+
+#include <algorithm>
+#include <iterator>
+#include <type_traits>
+
+namespace functools
+{
+
+constexpr void return_void();
+
+template<typename t>
+using remove_qualifiers = std::remove_reference_t<std::remove_cv_t<t>>;
+
+template<typename seq_, typename = void>
+struct reserver_
+{
+    static inline void maybe_reserve_space(seq_&, unsigned)
+    {
+        //qDebug() << "nada";
+    }
+};
+
+template<typename seq_>
+struct reserver_<seq_, decltype(std::declval<seq_>().reserve(0u), return_void())>
+{
+    static inline void maybe_reserve_space(seq_& seq, unsigned sz)
+    {
+        seq.reserve(sz);
+    }
+};
+
+template<typename seq_>
+inline void maybe_reserve_space(seq_& seq, unsigned sz)
+{
+    reserver_<seq_, void>::maybe_reserve_space(seq, sz);
+}
+
+} // ns
+
+template<typename seq_, typename F>
+auto map(F&& fun, const seq_& seq)
+{
+    using seq_type = functools::remove_qualifiers<seq_>;
+
+    seq_type ret;
+    std::back_insert_iterator<seq_type> it = std::back_inserter(ret);
+
+    for (const auto& elt : seq)
+        it = fun(elt);
+
+    return ret;
+}
+
+template<typename seq_, typename F>
+auto remove_if_not(F&& fun, const seq_& seq)
+{
+    using namespace functools;
+
+    using seq_type = remove_qualifiers<seq_>;
+    using value_type = typename std::iterator_traits<decltype(std::begin(std::declval<seq_>()))>::value_type;
+    using fun_ret_type = decltype(fun(std::declval<const value_type&>()));
+    static_assert(std::is_convertible<fun_ret_type, bool>::value, "must return bool");
+
+    seq_type ret;
+    maybe_reserve_space(ret, seq.size());
+
+    std::back_insert_iterator<seq_type> it = std::back_inserter(ret);
+
+    for (const value_type& elt : seq)
+        if (fun(elt))
+            it = elt;
+
+    return ret;
+}