Roland Conybeare
8f8be31584
subrepo: subdir: "xo-facet" merged: "ca53be82" upstream: origin: "git@github.com:Rconybea/xo-facet.git" branch: "main" commit: "ca53be82" git-subrepo: version: "0.4.9" origin: "???" commit: "???"
56 lines
1.9 KiB
ReStructuredText
56 lines
1.9 KiB
ReStructuredText
# xo-facet documentation master file
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xo-facet documentation
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======================
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xo-facet provides an object model that supports runtime polymorphism with interfaces and data kept separate.
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Design operates on similar lines to rust traits, haskell type clases, and go interfaces.
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Principles
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----------
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* Keep interfaces and data structures separate.
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An object is represented using a combination of exactly two pointers:
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an interface pointer and a data pointer.
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* An interface pointer implements an abstract facet.
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A facet has only abstract methods, and no state.
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* An interface pointer is analogous to a vtable pointer in a regular
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c++ object. It identifies a suite of related functions that operate
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on a particular data type.
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* A data pointer is like a pointer to a c struct.
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Data objects are passive, except for necessary ctors/dtors.
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Runtime polymorphism works seamlessly across different data types
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without requiring any prearrangement such as sharing a common
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base class.
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* We make 'familiar c++ objects', on demand, by pairing an interface pointer
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with a data pointer. Unlike usual c++ practice, we expect such objects
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to be transient. To represent persistent state, we rely
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solely on data pointers.
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* Since interface+data are separate,
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we can easily swap out one interface for another.
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This gives us several benefits:
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* A data type can easily particpate in polymorphism across different facets,
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without complicating object representation. To convert an object to use a
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different facet, we just swap out the interface pointer.
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* Interface and data pointers can arrive at the doorstep of a computation
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by different pathways. Often the pathway for an interface pointer is
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simpler that the pathway for a data pointer. This increases scope for
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devirtualization.
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.. toctree::
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:maxdepth: 2
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:caption: xo-facet contents
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implementation
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glossary
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genindex
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search
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