Add autopad_formatter and use it for the nullptr formatter

1 files changed, 84 insertions, 8 deletions

diff --git a/include/cxxformat/formatters.hpp b/include/cxxformat/formatters.hpp
index 515d0ec..119f7ea 100644
--- a/include/cxxformat/formatters.hpp
+++ b/include/cxxformat/formatters.hpp
@@ -22,18 +22,31 @@ namespace format {
 		}
 
 		template<typename Outputter>
-		constexpr void formatPadded(const format_output auto& out, Outputter&& outputter, std::size_t outputWidth, char padding, bool leftJustified, optional_int<std::size_t> minWidth)
+		constexpr void formatPadded(const format_output auto& out, Outputter&& outputter, std::size_t outputWidth, char padding, bool leftJustified, std::size_t minWidth)
 		{
-			if(outputWidth < minWidth.value_or(0) && !leftJustified)
+			if (!leftJustified && outputWidth < minWidth)
 			{
-				out(padding, *minWidth - outputWidth);
+				out(padding, minWidth - outputWidth);
 			}
 
 			outputter(out);
 
-			if(outputWidth < minWidth.value_or(0) && leftJustified)
+			if (leftJustified && outputWidth < minWidth)
 			{
-				out(padding, *minWidth - outputWidth);
+				out(padding, minWidth - outputWidth);
+			}
+		}
+
+		template<typename Outputter>
+		constexpr void formatPadded(const format_output auto& out, Outputter&& outputter, std::size_t outputWidth, char padding, bool leftJustified, optional_int<std::size_t> minWidth)
+		{
+			if (minWidth)
+			{
+				formatPadded(out, outputter, outputWidth, padding, leftJustified, *minWidth);
+			}
+			else
+			{
+				outputter(out);
 			}
 		}
 
@@ -159,6 +172,67 @@ namespace format {
 		}
 	}
 
+	template<typename Output>
+	class autopad_output : public FormatOutputBase<autopad_output<Output>> {
+		const Output& out;
+		std::size_t minWidth;
+		bool leftJustified;
+		char padding;
+#ifndef _NDEBUG
+		mutable bool used{false};
+#endif
+
+	public:
+		constexpr autopad_output(const Output& out, std::size_t minWidth, bool leftJustified, char padding) noexcept : out{out}, minWidth{minWidth}, leftJustified{leftJustified}, padding{padding} {}
+
+		void output(std::string_view what) const
+		{
+#ifndef _NDEBUG
+			assert(!used && "autopad_formatters must not call out() more than once for them to work correctly!");
+			used = true;
+#endif
+
+			formatPadded(out, what, leftJustified, padding, minWidth);
+		}
+	};
+
+	// padding of '\0' means take from spec
+	template<typename T, typename Derived, char padding = '\0'>
+	struct autopad_formatter {
+		template<typename U>
+		static constexpr void format(const format_output auto& out, U&& u, format_specifier spec, optional_int<std::size_t> minWidth, optional_int<std::size_t> precision)
+		{
+#ifdef _NDEBUG
+			if (minWidth)
+			{
+				Derived::formatAutopad(autopad_output{out, *minWidth, spec.flags.leftJustified, padding_(spec)}, std::forward<U>(u), spec, precision);
+			}
+			else
+			{
+				Derived::formatAutopad(out, std::forward<U>(u), spec, precision);
+			}
+#else
+			Derived::formatAutopad(autopad_output{out, minWidth.value_or(0), spec.flags.leftJustified, padding_(spec)}, std::forward<U>(u), spec, precision);
+#endif
+		}
+
+	private:
+		static constexpr char padding_([[maybe_unused]] format_specifier spec) noexcept
+		{
+			static_assert(std::derived_from<Derived, autopad_formatter<T, Derived, padding>>, "autopad_formatter must be used with CRTP");
+			static_assert(requires(T t, autopad_output<NullOutput> o, optional_int<std::size_t> p, format_specifier s) { Derived::formatAutopad(o, t, s, p); }, "The derived class must implement the static method formatAutopad(const format_output auto&, T-compatible, format_specifier, optional_int<std::size_t>)");
+
+			if constexpr (padding == '\0')
+			{
+				return spec.padding;
+			}
+			else
+			{
+				return padding;
+			}
+		}
+	};
+
 	using invalid_argument = std::invalid_argument;
 
 	template<std::integral T>
@@ -629,10 +703,10 @@ namespace format {
 	};
 
 	template<>
-	struct formatter<std::nullptr_t> {
-		static constexpr void format(const format_output auto& out, std::nullptr_t, format_specifier spec, optional_int<std::size_t> minWidth, optional_int<std::size_t>)
+	struct formatter<std::nullptr_t> : autopad_formatter<std::nullptr_t, formatter<std::nullptr_t>, ' '> {
+		static constexpr void formatAutopad(const format_output auto& out, std::nullptr_t, format_specifier, optional_int<std::size_t>)
 		{
-			formatPadded(out, "(nil)", ' ', spec.flags.leftJustified, minWidth);
+			out("(nil)");
 		}
 
 		static constexpr void conversionSupported(format_specifier spec)
@@ -641,6 +715,8 @@ namespace format {
 		}
 	};
 
+	static_assert(has_formatter<std::nullptr_t>);
+
 	template<>
 	struct formatter<const char*> {
 		static constexpr void format(const format_output auto& out, const char* s, format_specifier spec, optional_int<std::size_t> minWidth, optional_int<std::size_t> precision)