this was a design decision, but now I myself run into that obvious mistake;
thus not sure if this is a good design, or if we need a dedicated operation
to finish the builder and retrieve the iterable result.
as it turned out, when "inheriting" ctors, C++14 removes the base classes' copy ctors.
C++17 will rectify that. Thus for now we need to define explicitly that
we'll accept the base for initialising the derived. But we need do so
only on one location, namely the most down in the chain.
Since this now requires to import iter-adapter-stl.hpp and iter-source.hpp
at the same time, I decided to drop the convenience imports of the STL adapters
into namespace lib. There is no reason to prefer the IterSource-based adapters
over the iter-adapter-stl.hpp variants of the same functionality.
Thus better always import them explicitly at usage site.
...actual implementation of the planned IterSource packaging is only stubbed.
But I needed to redeclare a lot of ctors, which doesn't seem logical
And I get a bad function invocation from another test case which worked correct beforehand.
We need a way for higher layers to discard their caching and re-evaluate,
once some expansion layer was invoked to replace the current element with
its (functionally defined) "children" -- otherwise the first child will
remain obscured by what was there beforehand.
Solution is to pass such manipulation calls through the full chain of
decorators, allowing them to refresh themselves when necessary. To achieve
that technially, we add a base layer to absorb any such call passed down
through the whole decorator chain -- since we can not assume that the
parent, the original source core implements those manipualation calls
like expandChildren()
due to switching from ADL extension points to member functions,
we now need to detect a "state core" type in a different fashion.
The specific twist is that we can not spell out the full signature
in all cases, since the result type will be formed as a consequence
of this type detection. Thus there are now additional detectors to
probe for the presence of a specific function name only, and the
distinction between members and member functions has been sharpened.
Considering the fact that we are bound to introduce yet another iteration control function,
because there is literally no other way to cause a refresh within the IterTreeExplorer-Layers,
it is indicated to reconsider the way how IterStateWrapper attaches to the
iteration control API.
As it turns out, we'll never need an ADL-free function here;
and it seems fully adequate to require all "state core" objects to expose
the API as argument less member function. Because these reflect precisely
the contract of a "state core", so why not have them as member functions.
And as a nice extra, the implementation becomes way more concise in
all the cases refactored with this changeset!
Yet still, we stick to the basic design, *not* relying on virtual functions.
So this is a typical example of a Type Class (or "Concept" in C++ terminology)
- always layer the TreeExplorer (builder) on top of the stack
- always intersperse an IterableDecorator in between adjacent layers
- consequently...
* each layer implementation is now a "state core"
* and the source is now always a Lumiera Iterator
This greatly simplifies all the type rebindings and avoids the
ambiguities in argument converison. Basically now we can always convert
down, and we just need to pick the result type of the bound functor.
Downside is we have now always an adaptation wrapper in between,
but we can assume the compiler is able to optimise such inline
accessors away without overhead.
...yet this seems like a rather bad idea,
it breeds various problems and requires arcane trickery to make it fly
==> abandon this design
==> always intersperse an IterableDecorator between each pair of Layers
...especially relevant in the context of TreeExplorer,
where the general understanding is that the "Data Source" (whatever it is)
will be piggy-backed into the pipeline builder, and this wrapping is
conceived as being essentially a no-op.
It is quite possible we'll even start using such pipeline builders
in concert with move-only types. Just consider a UI-navigator state
hooked up with a massive implementation internal pointer tree attached
to all of the major widgets in the UI. Nothing you want to copy in passing by.
As it turned out, we had two bugs luring in the code base,
with the happy result of one cancelling out the adverse effects of the other
:-D
- a mistake in the invocation of the Itertools (transform, filter,...)
caused them to move and consume any input passed by forwarding, instead
of consuming only the RValue references.
- but util::join did an extraneous copy on its data source, meaning that
in all relevant cases where a *copy* got passed into the Itertools,
only that spurious temporary was consumed by Bug #1.
(Note that most usages of Itertools rely on RValues anyway, since the whole
point of Itertools is to write concise in-line transformation pipelines...)
*** Added additional testcode to prove util::stringify() behaves correct
now in all cases.
Obsoletes and replaces the ad-hoc written type rebindings from
iter-adapter and friends. The new scheme is more consistent and does
less magic, which necessitates an additional remove_pointer<IT> within
the iterator adaptors. Rationale is, "pointer" is treated now just as
a primitive type without additional magic or unwrapping, since it is
impossible to tell generically if the pointer or the pointee was
meant to be the "value"
Oh well.
This kept me busy a whole day long -- and someone less stubborn like myself
would probably supect a "compiler bug" or put the blame on the language C++
So to stress this point: the compiler behaved CORRECT
Just SFINAE is dangerous stuff: the metafunction I concieved yesterday requires
a complete type, yet, under rather specific circumstances, when instantiating
mutually dependent templates (in our case lib::diff::Record<GenNode> is a
recursive type), the distinction between "complete" and "incomplete"
becomes blurry, and depends on the processing order. Which gave the
misleading impression as if there was a side-effect where the presence
of one definition changes the meaning of another one used in the same
program. What happened in fact was just that the evaluation order was
changed, causing the metafunction to fail silently, thus picking
another specialisation.
- we do strip references
- we delegate to nested typedefs
Hoever, we do *not* treat const or pointers in any way special --
if the user want to strip or level these, he has to do so explicitly.
Initially it seemed like a good idea to do something clever here, but
on the long run, such "special treatment" is just good for surprises
...automatically whenever those are present.
Up to now, we hat that as base case, which limited usage to those cases
where we already know such nested definitions are actually present
attempt to re-use the same traits as much as possible
NOTE: new code not passing compiler yet, but refactored old code
does, and still passes unit test
this is a subtle change which, given all interfaces were used in a logically
consistent way, should not cause any observable change to the yielded elements.
But it changes runtime behaviour, insofar now the evalutaion is initiated
lazily, when first requesting a result type. Prior to this change, the
constructor immediately issued a call to the yield() extension point,
which presumably has the side-effect of preparing the core and initiating
any embedded evaluation, in order to get at the first result; it might
even detect an empty state.
Given the fact that all access operations on the iterator front-end perform
an empty check (and possibly throw at that point), this call is redundant.
surprising behaviour encountered while covering more cases
...obviously the return type of ExpandFunctor::operator()
was inferred as value, even while the invoked functor, from which
this type was deduced, clearly returns a reference.
Solution is simple not to rely on inference, moreover since we know
the exact type in the enclosing scope, thanks to the refactoring which
made this ExpandFunctor a nested class
NOTE:
as it turned out, this is not a compiler bug,
but works as defined by the language:
on return type inference, the detected type is decayed,
which usually helps to prevent returning a reference to a temporary
...while this implementation works now, it is still very complex and intricate.
I am still doubtful this is a good approach, but well, we need to try that route....
but possible only for the iterator -> iterator case
Since we can not "probe" a generic lambda, we get only one shot:
we can try to bind it into a std::function with the assumed signature
This is a consequence of the experiments with generic lambdas.
Up to now, lib::meta::_Fun<F> failed with a compilation error
when passing the decltype of such a generic lambda.
The new behaviour is to pick the empty specialisation (std::false_type) in such cases,
allowing to guard explicit specialisations when no suitable functor type
is passed
Basically we want to support two distinct cases, just by slightly adapting
the invocation of the expansion functor:
Case-1: classical monadic flatMap:
the Functor accepts a value yielded by the source iterator
and builds a new "expaneded" iterator
Case-2: manipulation of opaque implementation state
the Functor knows internal details of the source iterator
and thus takes the source iterator as such as argument,
performs some manipulation and then builds a new sub-iterator
A soulution to reconcile those two distinct cases can be built
with the help of a generic lambda
this solution makes me feel somewhat queasy..
stacking several adaptors and wrappers and traits on top of each other.
Well, it type checks and passes the test, so let's trust functional programming
The plan is to use a monad-like scheme, but allow for a lot of leeway
with respect to the src and value types of the expand functor.
A key idea is to allow for a *different* state core than used in the source
...but does not work as intended:
* just forming an IterStateWrapper does not trigger SFINAE cleanly in all cases
* IterStateWrapper can be formed, even when some of the extension points are missing;
this will be uncovered only later, when actually using one of the operations
but beyond that, the basic type selection logic can work this way
Here, the tricky question remains, how to relate this evalutaion scheme
to the well known monadic handling of collections and iterators.
It seems, we can not yet decide upon that question, rather we should
first try to build a concrete implementation of the envisioned algorithm
and then reconsider the question later, to what extent this is "monadic"
This can be seen as a side track, but the hope is
by relying on some kind of monadic evaluation pattern, we'll be
able to to reconcile the IterExplorer draft from 2012 with the requirement
to keep the implementation of "tree position" entirely opaque.
The latter is mandatory in the use case here, since we must not intermingle
the algorithm to resolve UI-coordinates in any way with the code actually
navigating and accessing GTK widgets. Thus, we're forced to build some kind
of abstraction barrier, and this turns out to be surprisingly difficult.
...which can be helpful when a function usually returns a somewhat dressed-up iterator,
but needs to return a specific fixed value under some circumstances
- fix some warnings due to uninitialised members
(no real problem, since these members get assigned anyway)
- use a lambda as example function right in the test
- use move initialisation and the new util::join
up to now, we allowed only initialisation with a precisely matching type.
But this special case seems worth supporting, since it typically occurs
within the "object builder" syntax based on Rec::Mutator
Explicitly assuming that those functions are called solely from IterAdapter
and that they are implemented in a typical standard style, we're able to elide
two redundant calls to the checkPoint() function. Since checkPoint typically performs
some non-trivial checks, this has the potential of a significant performance improvement
- we check (and throw ITER_EXHAUST) anyway from operator++, so we know that pos is valid
- the iterate() function ensures checkPoint is invoked right after iterNext,
and thus the typical standard implementation of iterNext need not do the same
...since that is what it meant to be.
To allow this chance, I've now added a default ctor to lib::Literal,
defaulting to the Symbol::EMPTY (the interned empty string)
The class Literal is used as a thin wrapper to mark the fact that
some string parameter or value is assumed to be given *literally*
For the contract this indicates
- that storage is somewhere
- storage is not owned and managed by Literal
- yet storage guaranteed to exist during the whole lifetime of the program
- Literal can not be altered
- Literal is transparently convertible to const char *
Currently I am in the course of building some path abstraction, and for that
task it makes sense to hold an array of Literals (instead of pointers), just
because it expresses the intent way more clear. I do not see anything in the
above mentioned contract to prohibit a default constructed Literal, with the
empty string being the most obvious choice.
Note: there is the class Symbol, which derives from Literal. Symbol takes
arbitrary strings, but *interns* them into a static symbol table.
...under the assumption that the content is normalised,
which means
- leading NULL is changed to Symbol::EMPTY
- missing elements in the middle are marked as "*"
- trailing NULL in extension storage is handled by adjusting nominal extension size
after various fruitless attempts to rely somehow on the array variant of unique_ptr,
I ended up with a hand coded version of an heap allocated array, managed automatically
as it turned out, the solution from yesterday works only with uniform argument lists,
but not with arbitrarily mixed types. Moreover the whole trickery with the
indices was shitty -- better use a predicate decision on template argument level.
This simple solution somehow just didn't occur to me...
...still somewhat unsatisfactory, because
- no clear compile error message when invoking pickArg with insufficient arguments
- the default initialisation case in SelectVararg is duplicated and messy
some time ago we abandoned our own tuple type in favour of std::tuple
Since then, the helpers and ported utilities provide some generic helpers
to deal with variadic argument sequences, especially to build index sequences,
which in turn can be used to "pick" individual arguments from a variadic parameter pack.
The expectation is for this part of the support library gradually to grow and
in parts to replace the existing type sequence processing helpers. The expectation
is that we'll retain the basic type sequence, lib::meta::Types, but retrofit it
to rely on variadic arguments
since the adoption of C++11, we gradually transition our metaprogramming helpers
to support and rely on variadic template parameters. For the time being,
we just augment existing facilities when it comes in handy, yet some more
heavyweight lifting and overall clean-up remains to be done eventually.
we allow assignment to the element embedded within the wrapper.
Yet obviously we need specific implementations for assignment
to the container itself. Thus we define the templated
assignment operator such as to render the explicit specialisation
a better match than anything generated from the templated
operator
basically DiffMessage has a "take everything" ctor, which happens
to match on type DiffMessage itslef, since the latter is obviously
a Lumiera Forward Operator. Unfortunately the compiler now considers
this "take everyting" ctor as copy constructor. Worse even, such a
template generated ctor qualifies as "best match".
The result was, when just returing a DiffMessage by value form a
function, this erroneous "copy" operation was invoked, thus wrapping
the existing implementation into a WrappedLumieraIterator.
The only tangible symptom of this unwanted storage bloat was the fact
that our already materialised diagnostics where seemingly "gone". Indee
they weren't gone for real, just covered up under yet another layer of
DiffMessage wrapping another Lumiera Forward Iterator
by moving, we can avoid the generation of up to 3 additional shared copies
of the DataHandle. The whole invocation now works without touching any shared count
and thus without incurring a memory barrier...
this becomes more relevant now, since the actual MutationMessage iterators
are implemented in terms of a shared_ptr to IterSource. Thus, when building
processing pipelines, we most definitively want to move that smart-ptr into
the destination, since this avoids touching the shared count and thus avoids
generating unnecessary memory barriers.
...allows us to get rid of quite some boost-includes
Incidentally, "our own" implementation is equivalent to both the
boost implementation and the implementation from C++14
It is just a bit more concise to write.
since we do not want to increase the footprint, we're bound to reuse
an existing VTable -- so IterAdapter itself is our only option.
Unfortunately we'll need to pass that through one additional
decoration layer, which is here the iterator; to be able to
add our string conversion there, we need to turn that into
a derived class and add a call to access the underlying
container, which gets us into element type definition mess....
now this highlights the unsettled decision still the more,
as can be seen by all that unnecessary copying. Basically we move the
Diff into the lambda-closure, from there into an anonymous instance,
from there into the embedded Buffer in MutationMessage, which again
just happens to sit in the closure storage when the action is invoked.
And all of this copying just to move the DiffMessage for consumption
into the TreeMutator...
thus by #1066 we should really get rid of the MutationMessage class altogether!
actually I do not know much regarding the actual situation when,
within the Builder run, we're able to detect a change and generate
a diff description. However, as a first step, I'll pick IterSrouce
as a base interface and use a "generation context", which is to be
passed by shared-ptr
again surprising how such fundamental bugs can hide for years...
Here the reason is that IterAdapter leaves the representation of "NIL" to
its instantiation / users; some users (here in for example the ScopedCollection)
can choose to allow for different representations of "NIL", but the comparison
provided by IterAdapter just compares the embedded pos by face value.
seems like most usages will want to expose this kind of diagnostics for unit testing
and in fact the queue or stack nature is the primary nature of this entity,
while iterability comes as additional trait
- concept for a first preliminary implementation of dispatch into the UI thread
- define an integration effort to build a complete working communication chain
...again to make it work with GCC-5,
also to allow more leeway using various compilers
Explanation: we use a helper function to abbreviate the
demangled type names to make diagnostic ouput more readable.
Obviously such a function needs to be adjusted to the
way concrete compilers generate their type output; GCC-5
slightly differs to GCC-4.9 here, so I've made the regular
expressions a bit more flexible
we have a catch-all template operator to get a string converted
or pretty printed output from "any object". Unfortunately
this overload counts equivalent to another overload by
the IO manipulators. Solution is to define both operarators
similar in the first argument, thus turing the overload
for the IO manipulators into the more specific overload
due to the explicitly given second argument
this seems like an obvious functionality and basically harmless,
since commands are designed to be inherently stateful, which is reflected
in all the internal storage holders to expos an assignment operator
(even while the actual implementation is based on placement new instead
of assigning values into the storage, and thus even supports immutable
values). The only possible ramification is that argument values must
be default constructible
in accordance to the design changes concluded yesterday.
- in the standard cases we now check the global registry first
- automatically create anonymous clone copy from global commands
- reorganise code internally to use common tail implementation
this might turn into lock contention problem, but better optimise
a correct implementation than fix a fast yet broken one.
Hint: SessionCommandFunction_test demonstrates that the
symbol table can be corrupted by creating Symbol instances
in parallel without proper locking. So yes, this is for real.
since Symbol instance are now backed by a symbol table,
we can use a much faster hash function by just hashing the
pointer into the symbol table, since the Symbol string content
is already checked at initialisation.
Up to now, we tolerated null pointers in Literal instances.
But we can not tolerate passing a null cString to Symbol initialisation.
Rather, hereby we introduce a dedicated "bottom" Symbol, a valid "null object"
For this task, I've also investigated to use boost::operators
This would only incur a negligible penalty on build times and executable sizes,
however, I don't consider the boost based solution to improve readability,
since many of these comparisons are tricky or subtly different.
Moreover, since boost::operators needs to be mixed-in, the initialisation
of Symbol objects becomes difficult, not to mention the additional base class
information visible in the debugger when inspecting Symbol or Literal objects
For that reason, I decided *against* using Boost here and coded up
all the operators in all combinations manually
...which means, from now on identical input strings
will produce the same Symbol object (embedded pointer).
TODO: does not handle null pointers passed in as c-String properly
obsoleted by C++11
* in most cases, it can be replaced by an explicit conversion operator
* especially for the Lumiera Forward Iterators, we need an implicit conversion
This changeset fixes a huge pile of problems, as indicated in the
error log of the Doxygen run after merging all the recent Doxygen improvements
unfortunately, auto-linking does still not work at various places.
There is no clear indication what might be the problem.
Possibly the rather unstable Sqlite support in this Doxygen version
is the cause. Anyway, needs to be investigated further.
it is not *that* hard to behave in a somewhat sane manner here.
And even more: this *is* basically the symbol table implementation we need.
Thus we only need to build the right front-end now...
...otherwise our log will be flooded with command definition messages soon
NOTE: to see all command definitions happening, set into environment:
NOBUG_LOG='command:TRACE
...since there is not any test coverage for this trait, which
turned out to be quite deeply rooted in the system by now and
handles several rather subtle special cases
...and move the tail-call of the template instantiation into try.cpp
This experiment clearly shows the discrepancy now:
- binding a member pointer directly into a function object will expand the argument list
- but binding a similar lambda into a function object won't
(it is not necessary due to the context capture)
The result is that we need to drop support for one of those cases,
and it is clear that the member poiter will be the looser...
As a first step towards a gradual rework of our function metaprogramming helpers,
this change prepends a generic case for all kinds of functors to our existing
solution, which up to now was entirely based on explicit specialisations.
C++11 supplied the new language construct 'decltype(EXPR)', which allows us
to capture any class with an function operator, which also includes the Lambdas.
The solution was proposed 2011 on StackOverflow
http://stackoverflow.com/questions/7943525/is-it-possible-to-figure-out-the-parameter-type-and-return-type-of-a-lambda/7943765#7943765
We used it already with success within our TreeMutator.
But obviously the goal should be to unite all the function trait / metaprogramming helpers,
which unfortunately is a more expensive undertaking, since it also involves
to get rid of the explicit specialisations and retrofit our Types<XXX...> helper
to rely on variadic templates rather than on loki-style typelists.
This first step here is rather conservative, since we'll still rely on our
explicit specialisations in most cases. Only the Lambdas will go through the
new, generic case, and from there invoke the specialisation for member functions.
The latter need to be rectified as well, which is subject of the next changeset...
Writing and debugging such tests is always an interesting challenge...
Fortunately this exercise didn't unveil any problem in the newly written
code, only some insidious problems in the test fixture itself. Which
again highlights the necessity, that each *command instance* needs
to be an independent clone from the original *command prototype*,
since argument binding messages and trigger messages can appear
in arbitrary order.
This is a little bit of functionality needed again and again;
first I thought to use the TypedCounter, but this would be overkill,
since we do not actually need different instances, and we do not need
to select by type when incrementing the counter. In fact, we do not
even need anything beyond just allocating a number.
So I made a new class, which can be used RAII style
this was a spin-off activity from writing the SessionCommand
function(integration) test, where I noted that we can't just
capture "a time value" as command memento
basically this is not necessary, since the compiler figures out
to use the conversion to target type when attempting to resolve
an equality comparison. But it helps to avoid ambiguities in cases
where several conversion paths do exist, e.g. when comparing string
with C-string
explicitly observed with the debugger that the call path is sane;
the code looks innocuous, but it is quite magic how the compiler
picks precisely the right ctors and inserts conversions apropriately
From a purely logical viewpoint, it looked sensible to require an actual
value for an offset, especially since our time values are immutable.
But this has the unfortunate consequence that we'd be unable to use
an offset value as parameter for any command, since we store the arguments
as tuple and the tuple type has a default constructor. We might be able
to get around that problem, but such looks brittle to me; it is just
plain surprising for anyone not familiar with the internals of the
command system.
For that reason, I've now added a default ctor to the Offset type
...since the session loop will be notified on any change via the
interface, adding a command will activate the loop, and the builder
timeout is handled separately via the dirty state. So there is no
need to spin around the loop in idle state.
As a aside, timeout waiting on a condition variable can be intentional
and should thus not be logged as an error automatically. It is up to the
calling context to decide if a timeout constitutes an exceptional situation.
It is always a trade-off performance vs. readability.
Sometimes a single-threaded implementation of self-contained logic
is preferable to a slightly more performant yet obscure implementation
based on our threadpool and scheduler.
Did a full review of state and locking logic, seems airtight now.
- command processing itself is unimplemented, we log a TODO message for now
- likewise, builder is not implemented
- need to add the deadlock safeguard #1054
And yes, this warning is for real, while the compiler has no way
to decide if there is actual danger lurking. A type with internal
linkage (e.g. defined in an anonymous namespace) will be treated
by the linker as a separate entity on each encounter (i.e. in
each distinct compilation unit). When multiple translation units
start collaborating on such a type, they *might* be referring
to different memory locations, while semantically the intention
is to refer to the same location.
And since we're dealing with a library facility here, *we* have
likewise now power to ensure proper usage, so we better be cautious.
after reading some related code, I am leaning towards a design
to mirror the way command messages are sent over the UI-Bus.
Unfortunately this pretty much abandons the possibility to
invoke these operations from a client written in C or any
other hand made language binding. Which pretty much confirms
my initial reservation towards such an excessively open
and generic interface system.
...the sheer amount of mechanical replacements scattered all over these
files might be a vivid indication, that the design of the interface system
is subobptimal ;-)
Phew, convoluted.
And I was doubtful that we need to support multiple typed child collection
Well, we get three such collections already in the first real world example...
reason is, only files with a @file comment will be processed
with further documentation commands. For this reason, our Doxygen
documentation is lacking a lot of entries.
HOWTO:
find src -type f \( -name '*.cpp' -or -name '*.hpp' \) -not -exec egrep -q '\*.+@file' {} \; -print -exec sed -i -r -e'\_\*/_,$ { 1,+0 a\
\
\
/** @file §§§\
** TODO §§§\
*/
}' {} \;
Damn sideeffect of the suppport for move-only types: since we're
moving our binding now into place /after/ construction, in some cases
the end() iterator (embedded in RangeIter) becomes invalid. Indeed this
was always broken, but didn't hurt, as long as we only used vectors.
Solution: use a dedicated init() hook, which needs to be invoked
*after* the TreeMutator has been constructed and moved into the final
location in the stack buffer.
unintentionally we used copy construction in the builder expression,
wenn passing in the CollectionBinding to the ChildCollectionMutator.
The problem is that CollectionBinding owns a shaddow buffer, where
the contents of the target collection are moved temporarily while
applying the diff. The standard implementation of copy construction
would cause a copy of that shaddow buffer, which boils down to
a copy of the storage of the target collection.
If we want to support move-only types in the collection, most notably
std::unique_ptr, we can thus only use the move constructor. Beyond that
there is no problem, since we're only ever moving elements, and new
elements will be move constructed via emplace() or emplace_back()
actually this is a pragmatic extension for some special use cases,
and in general rather discurraged, since it contradicts the
established diff semantics. Yet with some precaution, it should
be possible to transport information via an intermediary ETD
Map -> ETD -> Map
for the record: while it is indeed sweet-and-simple to support Ref::THIS
here, it is near impossible to represent it in general, in a setup with
multiple "onion-layers". The reason is, we'd have to incorporate such
special treatment into the /selector predicate/, which in turn undermines
the ability to pick the right onion layer to handle a given diff verb,
since "Ref::THIS" is a generic marker and we have no other data to base
the decision in the selector on.
Up to now, InPlaceBuffer used to default construct an instance of the
Interface class, and then you'd need to invoke the `create()` function
to actually create the desired subclass. This is not only inefficient,
but rules out the use of abstract interfaces / base classes.
Unfortunately, there is no way in C++ to specify an explicit template argument list
on ctor calls, so we resort to the trick of passing an additional dummy marker argument
