49 lines
1.4 KiB
Nim
49 lines
1.4 KiB
Nim
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####################################################################################################
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# Base delegate.
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type Delegate = ref object of RootObj
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nil
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method thing(d: Delegate): string {.base.} =
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## Default implementation of "thing".
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## Using a method rather than a proc allows dynamic dispatch.
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"default implementation"
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####################################################################################################
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# Delegator.
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type Delegator = object
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delegate: Delegate
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proc initDelegator(d: Delegate = nil): Delegator =
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## Create a delegator with given delegate or nil.
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if d.isNil:
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Delegator(delegate: Delegate()) # Will use a default delegate instance.
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else:
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Delegator(delegate: d) # Use the provided delegate instance.
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proc operation(d: Delegator): string =
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## Calls the delegate.
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d.delegate.thing()
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####################################################################################################
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# Usage.
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let d = initDelegator()
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echo "Without any delegate: ", d.operation()
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type Delegate1 = ref object of Delegate
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let d1 = initDelegator(Delegate1())
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echo "With a delegate which desn’t provide the “thing” method: ", d1.operation()
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type Delegate2 = ref object of Delegate
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method thing(d: Delegate2): string =
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"delegate implementation"
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let d2 = initDelegator(Delegate2())
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echo "With a delegate which provided the “thing” method: ", d2.operation()
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