43 lines
2.2 KiB
Plaintext
43 lines
2.2 KiB
Plaintext
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@node Helpers
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@chapter Helpers
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The above chapters introduced you to various ns-3 programming concepts
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such as smart pointers for reference-counted memory management, attributes,
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namespaces, callbacks, etc. Users who work at this low-level API
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can interconnect ns-3 objects with fine granulariy. However, a
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simulation program written entirely using the low-level API would
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be quite long and tedious to code. For this reason, a separate so-called
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``helper API'' has been overlaid on the core ns-3 API. If you have read
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the ns-3 tutorial, you will already be familiar with the helper API,
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since it is the API that new users are typically introduced to first.
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In this chapter, we introduce the design philosophy of the helper
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API and contrast it to the low-level API. If you become a heavy
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user of ns-3, you will likely move back and forth between these
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APIs even in the same program.
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The helper API has a few goals:
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@enumerate
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@item the rest of @code{src/} has no dependencies on the helper API;
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anything that can be done with the helper API can be coded also at
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the low-level API
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@item @strong{Containers:} Often simulations will need to do
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a number of identical actions to groups of objects. The helper
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API makes heavy use of containers of similar objects to which similar
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or identical operations can be performed.
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@item The helper API is not generic; it does not strive to maximize
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code reuse. So, programming constructs such as polymorphism and
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templates that achieve code reuse are not as prevalent. For instance,
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there are separate CsmaNetDevice helpers and PointToPointNetDevice
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helpers but they do not derive from a common NetDevice base class.
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@item The helper API typically works with stack-allocated (vs.
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heap-allocated) objects. For some programs, ns-3 users may not
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need to worry about any low level Object Create or Ptr handling;
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they can make do with containers of objects and stack-allocated helpers
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that operate on them.
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@end enumerate
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The helper API is really all about making ns-3 programs easier to
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write and read, without taking away the power of the low-level
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interface. The rest of this chapter provides some examples of
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the programming conventions of the helper API.
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