Delegates: Difference between revisions

{{out}}

<pre>default implementation

default implementation

delegate implementation</pre>

=={{header|NGS}}==

<lang NGS>{

type Delegator

F init(d:Delegator) d.delegate = null

F default_impl(d:Delegator) 'default implementation'

F operation(d:Delegator) default_impl(d)

F operation(d:Delegator) {

guard defined thing

guard thing is Fun

try {

d.delegate.thing()

}

catch(e:ImplNotFound) {

# Might be unrelated exception, so check and optionally rethrow

e.callable !== thing throws e

default_impl(d)

}

}

F operation(d:Delegator) {

guard d.delegate is Null

default_impl(d)

}

a = Delegator()

echo(a.operation())

# There is no method thing(s:Str)

a.delegate = "abc"

echo(a.operation())

# ... now there is method thing(s:Str)

F thing(s:Str) 'delegate implementation'

echo(a.operation())

}</lang>