Add util::at helper

libs/util/include/psemek/util/at.hpp

@@ -0,0 +1,53 @@
+#pragma once
+
+#include <psemek/util/exception.hpp>
+#include <psemek/util/to_string.hpp>
+
+#include <vector>
+
+namespace psemek::util
+{
+
+	struct key_error_base
+		: exception
+	{
+		using exception::exception;
+	};
+
+	template <typename Key>
+	struct key_error
+		: key_error_base
+	{
+		key_error(Key const & key, boost::stacktrace::stacktrace stacktrace = {})
+			: key_error_base(util::to_string("no such key: ", key), std::move(stacktrace))
+			, key_(key)
+		{}
+
+		Key const & key() const
+		{
+			return key_;
+		}
+
+	private:
+		Key key_;
+	};
+
+	template <typename Container, typename Key>
+	auto & at(Container && container, Key const & key)
+	{
+		if (auto it = container.find(key); it != container.end())
+			return it->second;
+
+		throw key_error<Key>(key);
+	}
+
+	template <typename T, typename Key>
+	auto & at(std::vector<T> && container, Key const & key)
+	{
+		if (key < container.size())
+			return container[key];
+
+		throw key_error<Key>(key);
+	}
+
+}