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copied!<p>I guess the obvious choices are:</p> <p>o Switch to a transient data structure (builder) for the update. This is quite normal. <code>StringBuilder</code> for <code>String</code> manipulation for example. As your example.</p> <pre><code>Person p3 = Builder.update(p) .withAddress( Builder.update(p.address()) .withCity("Berlin") .build() ) .build(); </code></pre> <p>o Always use persistent structures. Although there appears to be lots of copying, you should actually be sharing almost all state, so it is nowhere near as bad as it looks.</p> <pre><code>final Person p3 = p .withAddress( p.address().withCity("Berlin") ); </code></pre> <p>o Explode the data structure into lots of variables and recombine with one huge and confusing constructor.</p> <pre><code>final Person p3 = Person.of( p.name(), Address.of( p.house(), p.street(), "Berlin", p.country() ), p.x(), p.y(), p.z() ); </code></pre> <p>o Use call back interfaces to provide the new data. Even more boilerplate.</p> <pre><code>final Person p3 = Person.of(new PersonInfo( public String name () { return p.name(); ) public Address address() { return Address.of(new AddressInfo() { private final Address a = p.address(); public String house () { return a.house() ; } public String street () { return a.street() ; } public String city () { return "Berlin" ; } public String country() { return a.country(); } })), public Xxx x() { return p.x(); } public Yyy y() { return p.y(); } public Zzz z() { return p.z(); } }); </code></pre> <p>o Use nasty hacks to make fields transiently available to code.</p> <pre><code>final Person p3 = new PersonExploder(p) {{ a = new AddressExploder(a) {{ city = "Berlin"; }}.get(); }}.get(); </code></pre> <p>(Funnily enough I was just put down a copy of Purely Functional Data Structures by Chris Okasaki.)</p>

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