From f1a2e3472e61b8d6c3b3d0159a859f1c41654028 Mon Sep 17 00:00:00 2001
From: Jupp Tscheak <jupp.tscheak@daimler.com>
Date: Thu, 15 Jul 2021 15:47:27 +0200
Subject: [PATCH] Interface function IEntityRepository::Get is returning an
optional reference to query an IEntity.
In order to check whether an IEntity with a certain name/id exists, function IEntityRepository::Contains could be used to query this information. If IEntityRepository::Get is called on a non-existing name/id, the function would throw, so for defensive programming reasons a IEntityRepository::Contains should always be done before actually calling IEntityRepository::Get. The good thing about plain old C-pointers is that assignment and existence check can be done in one call. Since C++17 the same functionality is managed by std::optional.
Another disadvantage of using a plain reference to IEntity is when it is used as a class member, where it needs to be initialized when an object of that class is defined. It might be that during construction time this IEntity is not known/existing yet. Of cource, a plain old C-pointer could be used in this case, but it wouldn't be a consistant usage.
The proposal is to use std::optional<std::reference_wrapper<IEntity>> as return value for IEntityRepository::Get.
Signed-off-by: Jupp Tscheak <jupp.tscheak@daimler.com>
---
MantleAPI/include/MantleAPI/Traffic/i_entity_repository.h | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/MantleAPI/include/MantleAPI/Traffic/i_entity_repository.h b/MantleAPI/include/MantleAPI/Traffic/i_entity_repository.h
index 38e865e3..bcc1bb1c 100644
--- a/MantleAPI/include/MantleAPI/Traffic/i_entity_repository.h
+++ b/MantleAPI/include/MantleAPI/Traffic/i_entity_repository.h
@@ -18,6 +18,8 @@
#include <MantleAPI/Traffic/entity_properties.h>
#include <MantleAPI/Traffic/i_entity.h>
+#include <functional>
+#include <optional>
#include <string>
#include <vector>
@@ -35,8 +37,8 @@ class IEntityRepository
virtual IStaticObject& Create(UniqueId id, const std::string& name, const StaticObjectProperties& properties) = 0;
virtual IVehicle& GetHost() = 0;
- virtual IEntity& Get(const std::string& name) = 0;
- virtual IEntity& Get(UniqueId id) = 0;
+ virtual std::optional<std::reference_wrapper<IEntity>> Get(const std::string& name) = 0;
+ virtual std::optional<std::reference_wrapper<IEntity>> Get(UniqueId id) = 0;
virtual bool Contains(UniqueId id) const = 0;
virtual void Delete(const std::string& name) = 0;
--
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