It should also be noted that in the case of policies, the public inheritance does not represent an is-a relationship between the host and the policy classes. Email Required, but never shown. Exciting stuff, but also rather daunting. The article mentioned above gives the following answer: You want to use a library that the next programmer is going to know and that is going to be well supported in the future - so you pick a major lib. The book has been republished and translated into several languages since Sign up or log in Sign up using Google. 
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Loki | Main / HomePage
Charles Anderson Charles Anderson 8, 13 13 gold badges 50 50 silver badges 66 66 bronze badges. Loii MPL metafunctions, however, the output is usually represented by the instantiated host class itself, rather than a nested output type.
Martin Beckett Martin Beckett Message ; using OutputPolicy:: Active 7 years, 2 months ago. Speaking as someone who's used quite a bit of the Boost library, and also looked at Loki more than once, the biggest problem was the sparsity of documentation. It just felt more natural to me to use the loki's smart pointer then boost's one.
This makes it harder to pass values between those subsystems: It should also be noted that in the alexabdrescu of policies, the public inheritance does not represent an is-a relationship between the host and the policy classes. Retrieved from " https: Loki is not tied to the book anymore as it already has a lot of new components e.
I used Loki once for a little tool basically an interpreter and actually liked it. I actually prefer Loki's way of doing things and I have contributed to Loki myself a Decorator pattern which now sits in the tracker because the project as far as I know is no longer maintained. You want to use a library that the next programmer is going to know and that is going to be well supported in the future - so you pick a major lib.
A notable feature of this aspect of the policy idiom is that, relative to object-oriented programmingpolicies invert the relationship between base class and derived class - whereas in OOP interfaces are traditionally represented by abstract base classes and implementations of interfaces by derived classes, in policy-based design the derived host class represents the interfaces and the base policy classes implement them.
Loki's suffers from being a good library touching on several functional areas template metaprogamming support with a few specific applications: Exciting stuff, but also rather daunting.
Alexandrescu pushes new ideas, other people adopt those for real world.
Sign up using Email and Password. Policy classes have some similarity to callbacksbut differ in that, rather than consisting of alexamdrescu single functiona policy class will typically contain several related functions methodsoften combined with state variables or other facilities such as nested types. Even in cases where no more than one implementation of each policy will ever be used, decomposing a class into policies can aid the design process, by increasing modularity and highlighting exactly where orthogonal design decisions have been made.
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While assembling software components alexahdrescu of interchangeable modules is a far from new concept, policy-based design represents an innovation in the way it applies that concept at the relatively low level of defining the behavior of an individual class. That might be less convenient, but it discourages careless use of a poorly suited library and means you can really trust what is Standard. Loki inspired similar tools and functionality now also present in the Boost library collection.
Designers can easily write more OutputPolicy s by adding new classes with the member function Print and take those as new OutputPolicy s.
Alexandrescu able loki c library
Compiler vendors used Loki as a compatibility benchmark, further increasing the number of compliant compilers. No-one needs a smart pointer with 6 template parameters. Ongoing contributions by many people have improved the overall robustness and functionality of the library.
As Loki is a library of designs and not the design of a library, it should make minimum assumptions about its environment and provide appropriate hooks wherever some default decision is chosen.
Modern C++ Design - Wikipedia
How do we handle problem users? Graphic designers are able to give a name to their policies, which represent concepts, and not those which loik operations or minor implementation details.
Note that the generic implementation is in Run and therefore the code is unable to be compiled unless both policies Print and Message are provided. The contents are suitable for an overwhelming majority of uses, not hardcoding some arbitrary set of compromises that might only be good for a relatively small proportion of programs. The book has been republished and translated into several languages since
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