Ichthyostega
26bf32525b
* based on reproducible data in `TestFrame` * using Murmur64A hash-chaining to »mark« with a parameter This emulates the simplest case of 1:1 processing and can also be applied ''in-place''
117 lines
5.3 KiB
Text
117 lines
5.3 KiB
Text
how to crack nut #47
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====================
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:toc:
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.collection of successfully employed technical solutions
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Some nasty problems are recurring time and again. Maybe a trick could be found somewhere
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in the net, and a library function was created to settle this damn topic once and for all.
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Maybe even a nice test and demo is provided. And then the whole story will be forgotten.
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_Sounds familiar?_ => ☹☻☺ ~[red]#then please leave a note here...#~
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Methods
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-------
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Mathematics
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~~~~~~~~~~~
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- some basic descriptive statistics computation are defined in 'lib/stat/statistic.hpp'
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- the simple case for _linear regression_ is also implemented there
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- Gnuplot provides also common statistics functions, which may come in handy when the
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goal is anyway to create a visualisation (-> see <<investigation,below>>)
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Situations
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----------
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Investigation
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~~~~~~~~~~~~~
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summary test::
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Reformulate the research and the findings into a test, which can be read top-down like a novel.
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Start with documenting the basics, package helpers into a tool class, or package setup into a
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workbench-style class, with individual tool modules. Provide a short version of this test with
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the basic demo, which should be able to run with the regular test suite. Extended long-running
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tests can be started conditionally with commandline-arguments. See 'scheduler-stress-test.cpp'
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visualisation::
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Use code generation to visualise data structures or functions and observation statistics.
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Typically these generation statements can be packaged into an invocation helper and included
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into a relevant test, but commented-out there.
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+
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- generate Graphviz diagrams: 'lib/dot-gen.hpp' provides a simple DSL. See 'test-chain-load-test.cpp'
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- generate Gnuplot scripts: use the Text-Template engine to fill in data, possibly from a data table
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* 'lib/gnuplot-gen.hpp' provides some pre-canned scripts for statistics plots
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* used by the 'stress-test-rig.cpp', in combination with 'data.hpp' to collect measurement results
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Common Tasks
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------------
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Data handling
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~~~~~~~~~~~~~
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persistent data set::
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use the `lib::stat::DataTable` ('data.hpp') with CSV rendering -> see 'data-csv-test.cpp'
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Formatting
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~~~~~~~~~~
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- implement a conversion-to-string operator.
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- include the C++ IOStreams via 'lib/format-cout.hpp' -> this magically uses the `util::toString()`
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- for testing, temporarily include 'lib/test/diagnostic-output' and use the `SHOW_EXPR` macro.
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- use 'util::join' ('lib/format-util.hpp') to join arbitrary elements with `util::toString()` conversion
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- use _printf-style formatters_ from Boost-format. We provide a light-weight front-end via 'lib/format-string.hpp'
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* the heavyweight boost-format include is only required once, for 'lib/format-string.cpp'.
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* the templated front-end passes-through most basic types and types with string-conversion
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* all invocations are strictly error safe (never throw) and can thus be used from catch-handlers
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- use the *Text-Template* engine. See 'text-template-test.cpp'. Can be used with simple map bindings,
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but also from a `lib::GenNode` tree, or with a custom defined `DataSource` template
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Language constructs
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-------------------
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Templates
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~~~~~~~~~
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build-from-anything::
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use a templated constructor, possibly even with varargs
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+
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- use a _deduction guide_ to pick the right ctor and arguments -> see
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* `ThreadJoinable` in 'thread.hpp', 698
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* `DataSource<string>` specialisation only when argument can be converted to string,
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in 'text-template.hpp', 745
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- prevent shadowing of _automatically generated copy operations._
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See https://issues.lumiera.org/ticket/963[#963]. Based on the ``disable if'' SFINAE technique.
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A ready-made templated typedef `lib::metadisable_if_self` can be found in 'lib/meta/util.hpp'
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Varargs
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~~~~~~~
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pick and manipulate individually::
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The key trick is to define an _index sequence template,_ which can then be matched against
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a processing template for a single argument; and the latter can have partial specialisations
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+
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- see 'variadic-argument-picker-test.cpp'
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- but sometimes it is easier to use the tried and true technique of the Loki-Typelists, which
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can be programmed recursively, similar to LISP. The »bridge« is to unpack the variadic argument pack
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into the `lib::meta::Types<ARGS...>` ([yellow-background]#⚠ still broken in 2024#
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see https://issues.lumiera.org/ticket/987[#987], use `lib::meta::TySeq` from 'variadic-helper.hpp' as workaround...
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+
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apply functor to each::
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A common trick is to use `std::apply` in combination with a _fold-expression_
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- provided as `lib::meta::forEach` in 'lib/meta/util.hpp
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- The design of the `DataTable` with CSV-Formatting is based on this technique, see 'lib/stat/data.hpp'
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- 'test-rand-ontology.cpp' uses this in `manipulateFrame()` to accept an arbitrary number of input chains
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+
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unpack iterator into tuple::
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Under controlled conditions this is possible (even while it seems like time travel from the runtime into
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the compile-time domain). The number of results to extract from the iterator must be known at compile time,
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and the possible result types must be limited, so that a visitor can be used for double-dispatch.
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+
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- see tuple-record-init-test.cpp
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- used in 'command-simple-closure.hpp' to receive parameter values sent via UI-Bus and package them
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into a tuple for invocation of a Steam-Layer command.
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