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This file is part of Logtalk <https://logtalk.org/>  
Copyright 1998-2020 Paulo Moura <pmoura@logtalk.org>

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
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    http://www.apache.org/licenses/LICENSE-2.0

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Design pattern:
	Lazy initialization

Description:
	Delay creation of a required instance (accessed using a key)
	until the instance is requested.

This pattern can be used with both classes and prototypes. The description
above is from the Wikipedia page on this pattern:

https://en.wikipedia.org/wiki/Lazy_initialization

This pattern is not described in the GoF book. See the Wikipedia page for
details and references.

The sample implementation uses classes.
