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Delegates: Difference between revisions
→{{header|Nim}}
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default implementation
delegate implementation</pre>
=={{header|Nim}}==
<lang Nim>####################################################################################################
# Base delegate.
type Delegate = ref object of RootObj
nil
method thing(d: Delegate): string {.base.} =
## Default implementation of "thing".
## Using a method rather than a proc allows dynamic dispatch.
"default implementation"
####################################################################################################
# Delegator.
type Delegator = object
delegate: Delegate
proc initDelegator(d: Delegate = nil): Delegator =
## Create a delegator with given delegate or nil.
if d.isNil:
Delegator(delegate: Delegate()) # Will use a default delegate instance.
else:
Delegator(delegate: d) # Use the provided delegate instance.
proc operation(d: Delegator): string =
## Calls the delegate.
d.delegate.thing()
####################################################################################################
# Usage.
let d = initDelegator()
echo "Without any delegate: ", d.operation()
type Delegate1 = ref object of Delegate
let d1 = initDelegator(Delegate1())
echo "With a delegate which desn’t provide the “thing” method: ", d1.operation()
type Delegate2 = ref object of Delegate
method thing(d: Delegate2): string =
"delegate implementation"
let d2 = initDelegator(Delegate2())
echo "With a delegate which provided the “thing” method: ", d2.operation()</lang>
{{out}}
<pre>Without any delegate: default implementation
With a delegate which desn’t provide the “thing” method: default implementation
With a delegate which provided the “thing” method: delegate implementation</pre>
=={{header|Objeck}}==
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