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116 lines
2.6 KiB
Markdown
116 lines
2.6 KiB
Markdown
---
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title: "delegate_observable"
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---
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{{< callout type="info">}}
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Header: `delegate_observable.h`
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Since: `TBC`
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{{< /callout >}}
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`etl::delegate_observable` is a variation on the observer pattern idea, but using delegates as the callback mechanism.
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```cpp
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template <typename TNotification, size_t Max_Observers>
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class delegate_observable
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```
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`TNotification` is the notification type.
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`Max_Observers` is the maximum number of observers that can be handled.
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## Template deduction guide
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```cpp
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template <typename TNotification, typename... TDelegates>
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delegate_observable(TNotification, TDelegates...)
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-> delegate_observable<TNotification, sizeof...(TDelegates)>;
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```
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**Example**
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```cpp
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etl::delegate<void(int)> delegate1;
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etl::delegate<void(int)> delegate2;
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etl::delegate_observable observable(int{}, delegate1, delegate2);
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```
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## Public types
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| Type | Description |
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| ------------------- | ------------------------------------------- |
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| `delegate_type` | The type of delegate used in this observer. |
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| `size_type` | The type used internally for sizes. |
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| `notification_type` | The type of the notification. |
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## Construction
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```cpp
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ETL_CONSTEXPR14 delegate_observable()
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```
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**Description**
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Default constructor.
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---
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```cpp
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template <typename... TDelegate>
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ETL_CONSTEXPR14 delegate_observable(TDelegate&&... delegates)
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```
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**Description**
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Construct from a collection of observers.
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---
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```cpp
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template <typename... TDelegate>
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ETL_CONSTEXPR14 delegate_observable(notification_type, TDelegate&&... delegates)
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```
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**Description**
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Construct from notification type and a list of observers.
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Variant for template deduction guide.
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The notification value is ignored. It is here to allow deduction of the notification type for the template deduction guide.
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## Modifiers
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```cpp
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ETL_CONSTEXPR14 bool add_observer(delegate_type observer)
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```
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**Description**
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Add an observer to the list.
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**Return**
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`true` if the observer was removed, `false` if not.
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---
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```cpp
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ETL_CONSTEXPR14 bool remove_observer(const delegate_type& observer)
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```
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**Description**
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Remove a particular observer from the list.
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**Return**
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`true if the observer was removed, false if not.
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---
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```cpp
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ETL_CONSTEXPR14 void clear_observers()
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```
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**Description**
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Clear all observers.
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## Status
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```cpp
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ETL_CONSTEXPR14 size_type number_of_observers() const
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```
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**Return**
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The number of observers.
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## Notofication
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```cpp
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ETL_CONSTEXPR14 void notify_observers(notification_type n) const
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```
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**Description**
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Notify all of the observers, sending them the notification.
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