hypergraph i/o refined

Author: SpectraL519

include/gl/io/format.hpp

@@ -39,7 +39,17 @@ range_formatter(R&& r) -> range_formatter<std::views::all_t<R>>;
 
 template <std::ranges::range R>
 auto set_formatter(R&& range, std::string_view sep = ", ") {
-    return range_formatter{std::forward<R>(range), sep, "{", "}"};
+    using view_type = std::views::all_t<R>;
+    return range_formatter<view_type>{std::views::all(std::forward<R>(range)), sep, "{", "}"};
+}
+
+/// @todo Add an indent_width parameter
+template <std::ranges::range R>
+auto multiline_set_formatter(R&& range) {
+    using view_type = std::views::all_t<R>;
+    return range_formatter<view_type>{
+        std::views::all(std::forward<R>(range)), ",\n  ", "{\n  ", "\n}"
+    };
 }
 
 } // namespace gl::io

include/gl/io/options.hpp

@@ -39,6 +39,7 @@ inline const stream_options_manipulator without_properties = unset_options(
     {detail::option_bit::with_vertex_properties, detail::option_bit::with_connection_properties}
 );
 
+// TODO: rename to _spec_fmt
 inline const stream_options_manipulator enable_gsf =
     set_option(detail::option_bit::specification_fmt);
 inline const stream_options_manipulator disable_gsf =

include/hgl/hypergraph.hpp

@@ -761,7 +761,7 @@ class hypergraph final {
     struct hyperedge_formatter {
     public:
         const hypergraph& hg;
-        const hyperedge_type& hyperedge;
+        const hyperedge_type hyperedge;
 
         friend std::ostream& operator<<(std::ostream& os, const hyperedge_formatter& proxy)
         requires std::same_as<directional_tag, undirected_t>
@@ -946,10 +946,18 @@ class hypergraph final {
             for (const auto& vertex : this->vertices())
                 os << "  - " << vertex << '\n';
         }
+        else {
+            this->_write_implicit_vset(os) << '\n';
+        }
 
-        os << "hyperedges:\n";
-        for (const auto& edge : this->hyperedges())
-            os << "  - " << this->display(edge) << '\n';
+        if (this->size() == 0uz) {
+            os << "hyperedges: {}";
+        }
+        else {
+            os << "hyperedges:\n";
+            for (const auto& edge : this->hyperedges())
+                os << "  - " << this->display(edge) << '\n';
+        }
 
         return os;
     }
@@ -960,22 +968,38 @@ class hypergraph final {
         const bool with_v_props =
             io::is_option_set(os, with_vertex_properties)
             and traits::c_writable<vertex_properties_type>;
-        if (with_v_props) {
-            os << "V :";
-            for (const auto& vertex : this->vertices())
-                os << " " << vertex;
+        if (with_v_props)
+            os << "V = " << io::multiline_set_formatter(this->vertices()) << '\n';
+        else
+            this->_write_implicit_vset(os) << '\n';
+
+        if (this->size() == 0uz) {
+            os << "E = {}\n";
         }
         else {
-            os << "|V| = " << this->order();
-        }
+            auto hyperedges = std::views::transform(this->hyperedges(), [this](auto hyperedge) {
+                return this->display(hyperedge);
+            });
 
-        os << "\nE:\n";
-        for (const auto& edge : this->hyperedges())
-            os << this->display(edge) << '\n';
+            // TODO: set/multiline_set
+            os << "E = " << io::multiline_set_formatter(hyperedges) << '\n';
+        }
 
         return os;
     }
 
+    std::ostream& _write_implicit_vset(std::ostream& os) const {
+        const auto n = this->order();
+        if (n == 0uz)
+            return os << "V = {}";
+        if (n == 1uz)
+            return os << "V = {0}";
+        if (n == 2uz)
+            return os << "V = {0, 1}";
+
+        return os << "V = {0, ..., " << n - 1 << '}';
+    }
+
     // --- data members ---
 
     size_type _n_vertices = 0uz;

include/hgl/io.hpp

@@ -13,6 +13,7 @@
 
 namespace hgl::io {
 
+using gl::io::multiline_set_formatter;
 using gl::io::range_formatter;
 using gl::io::set_formatter;
 
@@ -42,6 +43,8 @@ inline const stream_options_manipulator with_hyperedge_properties =
 inline const stream_options_manipulator without_hyperedge_properties =
     unset_option(detail::option_bit::with_connection_properties);
 
+// TODO: spec fmt
+
 using gl::io::with_properties;
 using gl::io::without_properties;