Sealed classes and methods: Difference between revisions
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{{
;Definition
In [[wp:Object-oriented_programming|object-oriented programming]], a '''sealed''' or '''final class''' is one which cannot be inherited from.
Classes are sometimes made non-
Rather than sealing the entire class, it may be possible to just seal certain
;Task
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public:
explicit MovieWatcher(std::string_view name) : m_name{name}{}
{▼
}▼
virtual void EatPopcorn()
{
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public:
explicit ParentMovieWatcher(std::string_view name) : MovieWatcher{name} {}
};
// ChildMovieWatcher can be inherited from▼
class ChildMovieWatcher : public MovieWatcher▼
{
public:
explicit ChildMovieWatcher(std::string_view name)
: MovieWatcher{name}{}
// EatPopcorn() cannot be overridden because it is 'final'
▲ void WatchMovie() override
void EatPopcorn() final override▼
{
std::cout << m_name << " is
}
};
class YoungChildMovieWatcher : public ChildMovieWatcher
▲// ChildMovieWatcher can be inherited from
▲class ChildMovieWatcher : public MovieWatcher
{
public:
:
// WatchMovie() cannot be overridden because it is 'final'
void WatchMovie() final override
{
", you are too young to watch the movie.\n";
▲ std::cout << m_name << " likes the movie\n";
▲ }
▲ void EatPopcorn() override
▲ {
}
};
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int main()
{
// A container for the MovieWatcher base class objects
std::vector<std::unique_ptr<MovieWatcher>> movieWatchers;
// Add some movie wathcers
movieWatchers.emplace_back(new ParentMovieWatcher("Donald"));
movieWatchers.emplace_back(new ChildMovieWatcher("Lisa"
movieWatchers.emplace_back(new
// Send them to the movies
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{{out}}
<pre>
Donald is watching the movie
Lisa
Sorry, Fred, you are too young to watch the movie.
Donald is enjoying the popcorn
Lisa is eating too much popcorn
Fred is eating
</pre>
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<!--</syntaxhighlight>-->
Note however in Phix there is no possibility of invoking parent.watch_movie() from the else branch, because you have completely replaced that routine in the child instance. Should you want to share code in that kind of fashion you would need to give it a different and completely unambiguous name.
=={{header|Raku}}==
Raku doesn't have final class but [https://docs.raku.org/syntax/role Roles] is normally used to mimic the goal.
<syntaxhighlight lang="raku" line># 20240626 Raku programming solution
role MovieWatcherRole { has Str $.name;
method WatchMovie() { say "$.name is watching the movie" }
method EatPopcorn() { say "$.name is enjoying the popcorn" }
}
class MovieWatcher does MovieWatcherRole {
method new(Str $name) { self.bless(:$name) }
}
class ParentMovieWatcher is MovieWatcher {
method new(Str $name) { self.bless(:$name) }
}
role ChildMovieWatcherRole {
method EatPopcorn() { say "$.name is eating too much popcorn" }
}
class ChildMovieWatcher is MovieWatcher does ChildMovieWatcherRole {
method new(Str $name) { self.bless(:$name) }
}
role YoungChildMovieWatcherRole {
method WatchMovie() {
say "Sorry, $.name, you are too young to watch the movie.";
}
}
class YoungChildMovieWatcher is ChildMovieWatcher does YoungChildMovieWatcherRole {
method new(Str $name) { self.bless(:$name) }
}
for ParentMovieWatcher.new('Donald'),
ChildMovieWatcher.new('Lisa'),
YoungChildMovieWatcher.new('Fred')
{ .WatchMovie and .EatPopcorn }</syntaxhighlight>
You may [https://ato.pxeger.com/run?1=nVPBToNAED144ysmxKRtgpyNPVo9adLYg_G4wlBQ2Gl2FxvS8CVeetCf8uKvuLtAoIVIldNm9r15bx6z7x-Cveb7_WeuoovLr7NvQSnCPb0l-MhUEKN4MIUdxEzCSgk49znLcO4AQIYqphAszjKmMw2UrAC3QkEiYWtuE74GFSNkBuVqatnh3zC1pE1Agg_xkb9Q0fA3Fc7V_NJxgpRJeeAVQkI54L6jxnE7tXMYAauHaeQ_pyjl9KoudrovmUCuDjSSI81_dbcxX8dJGv7qdiQbpmwyRJDlQTwYT0-j599mNm7lb6M9Uc7X402Pdsfc6M-OuSIhCq_eNw8KykH_CztsYZrrU7Vc7Wb57ty26Iw_7MNk0C_aIE40fnIaEYmBJfINf7IgztJwMvPs3D3RCnSXSNZAhs1VuFuBupWzA78NFRgPwW-XCMrqndfPvXn2Pw Attempt This Online!]
=={{header|Wren}}==
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3. Using the 'is' operator (i.e. a ''is'' C) to detect the type of 'a' wouldn't work here as this would return 'true' if 'a' were either a 'C' object or an object of a subclass of 'C'. It is possible to spoof the 'is' operator by overriding its normal behavior, though this is definitely not recommended!
<syntaxhighlight lang="
construct new(name, age) {
_name = name
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