From 1752c8905693d10bf91aecf8855c3e7bdc041da5 Mon Sep 17 00:00:00 2001
From: Avril <flanchan@cumallover.me>
Date: Mon, 17 Apr 2023 03:36:34 +0100
Subject: [PATCH] `leven_diff()`: Added string literal overloads for comptime
 string comparison load and allocation reductions.
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Fortune for libexopt's current commit: Blessing − 吉
---
 include/leven.h | 17 ++++++++++++++++-
 include/util.hh |  5 +++--
 src/leven.cpp   |  4 ++++
 3 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/include/leven.h b/include/leven.h
index 3067af7..c9ee7cc 100644
--- a/include/leven.h
+++ b/include/leven.h
@@ -4,10 +4,12 @@
 #include "exopt.h"
 
 #ifdef __cplusplus
+//#include "util.hh"
 
 #include <string_view>
 #include <concepts>
 #include <vector>
+#include <array>
 #include <span>
 #include <tuple>
 
@@ -24,6 +26,7 @@ size_t _EO(leven_diff)(const char* _EO(restrict), const char* _EO(restrict), siz
 }
 
 namespace exopt { namespace util [[gnu::visibility("internal")]] {
+	template<size_t N =0> // NOTE: Do not change this manually //
 	constexpr auto leven_diff(std::string_view s1, std::string_view s2) noexcept {
 		const size_t 
 			m(s1.size()),
@@ -58,7 +61,9 @@ namespace exopt { namespace util [[gnu::visibility("internal")]] {
 			return costs[n];
 		};
 
-		if consteval {
+		if constexpr(N > 0) {
+			return work_on_d(std::array<size_t, N+1>{});
+		} else if consteval {
 			return work_on_d(std::vector<size_t>(n + 1));
 		} else {
 			thread_local static std::vector<size_t> d;
@@ -74,6 +79,16 @@ namespace exopt { namespace util [[gnu::visibility("internal")]] {
 		return leven_diff(str{sa}, str{sb});
 	}
 
+	template<size_t M, size_t N>
+	constexpr decltype(auto) leven_diff(const char (&sa)[M], const char (&sb)[N]) noexcept {
+		if constexpr(!N) return M;
+		else if constexpr(!M) return N;
+
+		else if constexpr(M < N) return N - M; //XXX: Are these lines correct?
+		else if constexpr(N < M) return M - N; // ^
+		else return leven_diff<N>(std::string_view{sa}, std::string_view{sb});
+	}
+
 } }
 #endif
 
diff --git a/include/util.hh b/include/util.hh
index 762517f..c97122e 100644
--- a/include/util.hh
+++ b/include/util.hh
@@ -1,16 +1,17 @@
 #pragma once
 
+#include <string_view>
 #include <utility>
 
 #include "exopt.h"
 
-#define _EO_CONSTANT_VALUE(X) ([] { \
+#define _EO_CONSTANT_VALUE(X) ([]() { \
 	struct { \
 		typedef decltype(X) comptime_constant_t; \
 		consteval operator comptime_constant_t() const noexcept { return (X); } \
 	} inner; \
 	return inner; \
-}())
+})()
 
 namespace exopt { namespace util [[gnu::visibility("internal")]] {
 	template<typename T, typename U>
diff --git a/src/leven.cpp b/src/leven.cpp
index 6feb917..a4fad89 100644
--- a/src/leven.cpp
+++ b/src/leven.cpp
@@ -1,4 +1,6 @@
 
+#include <string>
+
 #include <cstdlib>
 #include <cstring>
 
@@ -18,5 +20,7 @@ namespace exopt {
 	namespace util [[gnu::visibility("internal")]] {	
 		static_assert(leven_diff("hello world", "Hello World") == 2, "Levelshtein distance incorrect for non-matching strings");
 		static_assert(leven_diff("hello world", "hello world") == 0, "Levelshtein distance incorrect for matching strings");
+		static_assert(leven_diff("hello world", std::string_view{"hello world"}) == 0, "Levelshtein distance incorrect for matching string container type 1");
+		static_assert(leven_diff(std::string{"llo world"}, std::string_view{"hello world"}) == 2, "Levelshtein distance incorrect for matching string container type 2");
 	}
 }