[core.memory] view_bytes now works much better and is easier to maint…

…ain. also in the case image_info fails to parse image data properly, return a much more detailled error message

include/tz/core/memory.hpp

@@ -6,30 +6,38 @@
 
 namespace tz
 {
-	template<typename T> requires(std::is_standard_layout_v<T>)
-	std::span<const std::byte> view_bytes(const T& t)
+	template<typename T>
+	constexpr auto view_bytes(T&& t) -> std::conditional_t<std::is_const_v<T>, std::span<const std::byte>, std::span<std::byte>>
 	{
-		return std::as_bytes(std::span<const T>(&t, 1));
-	}
-
-	template<typename T> requires(std::is_standard_layout_v<T>)
-	std::span<std::byte> view_bytes(T& t)
-	{
-		return std::as_writable_bytes(std::span<T>(&t, 1));
-	}
-
-	template<std::ranges::contiguous_range R> requires(std::is_const_v<std::ranges::range_value_t<R>>)
-	std::span<const std::byte> view_bytes(R&& range)
-	{
-		using T = std::ranges::range_value_t<R>;
-		return std::as_bytes(std::span<const T>(std::ranges::begin(range), std::ranges::end(range)));
-	}
-
-	template<std::ranges::contiguous_range R>
-	std::span<std::byte> view_bytes(R&& range)
-	{
-		using T = std::ranges::range_value_t<R>;
-		return std::as_writable_bytes(std::span<T>(std::ranges::begin(range), std::ranges::end(range)));
+		if constexpr(requires{std::ranges::contiguous_range<T>;})
+		{
+			// we are a range	
+			using V = std::ranges::range_value_t<T>;
+			std::span<V> range{std::begin(t), std::end(t)};
+			if constexpr(std::is_const_v<V>)
+			{
+				return std::as_bytes(range);
+			}
+			else
+			{
+				return std::as_writable_bytes(range);
+			}
+		}
+		else
+		{
+			// we are not a range
+			static_assert(std::is_standard_layout_v<T>, "view_bytes must be provided a contiguous range or a standard-layout-type. You have provided neither.");
+			// we are a scalar-y value
+			std::span<T, 1> span{&t};
+			if constexpr(std::is_const_v<T>)
+			{
+				return std::as_bytes(span);
+			}
+			else
+			{
+				return std::as_writable_bytes(span);
+			}
+		}
 	}
 }
 

src/tz/io/image.cpp

@@ -3,6 +3,8 @@
 #define STBI_FAILURE_USERMSG
 #define STB_IMAGE_IMPLEMENTATION
 #include "stb_image.h"
+#include <vector>
+#include <algorithm>
 
 namespace tz::io
 {
@@ -12,7 +14,11 @@ namespace tz::io
 		int ok = stbi_info_from_memory(reinterpret_cast<const stbi_uc*>(img_file_data.data()), img_file_data.size_bytes(), &w, &h, &channels);
 		if(ok != 1)
 		{
-			UNERR(tz::error_code::precondition_failure, "bad image file data: {}", stbi_failure_reason());
+			std::vector<char> initial_snippet;
+			initial_snippet.resize(std::min(static_cast<std::size_t>(20), img_file_data.size_bytes()));
+			std::transform(img_file_data.begin(), img_file_data.begin() + initial_snippet.size(), initial_snippet.begin(), [](std::byte ch)->char{return static_cast<char>(ch);});
+
+			UNERR(tz::error_code::precondition_failure, "bad image file data. reason: {}\ndata snippet ({}): \"{}\"", stbi_failure_reason(), initial_snippet.size(), reinterpret_cast<char*>(initial_snippet.data()));
 		}
 
 		return image_header