Ichthyostega
738d9e5b67
...because swapping in the new standards-based implementation leads to compile failures on tests to cover out-of-bounds cases. Under the (wrong) assumption, that some mistake must be hidden in the Splice-metafunction, I first provided a complete test coverage; while the actual problem was right below my nose, and quite obvious... The old implementation, being based on a case distinction over the argument count, simply was not able even to notice excess arguments; other the new implementation, based on variadics and `std::apply`, which is fully generic and thus passes excess arguments to `std::bind` when a position beyond the actual argument list is specified to be closed. The old behaviour was to silently ignore such an out-of-bounds spec, and this can be reinstated by explicitly capping the prepared tuple of binders and actual arguments passed to `std::bind` Another question of course is, if being tolerant here is a good idea. And beyond that, function-closure.hpp is still terrifyingly complex, unorganised and use-case driven, to start with....
816 lines
30 KiB
C++
816 lines
30 KiB
C++
/*
|
||
FUNCTION-CLOSURE.hpp - metaprogramming tools for closing a function over given arguments
|
||
|
||
Copyright (C)
|
||
2009, Hermann Vosseler <Ichthyostega@web.de>
|
||
|
||
**Lumiera** is free software; you can redistribute it and/or modify it
|
||
under the terms of the GNU General Public License as published by the
|
||
Free Software Foundation; either version 2 of the License, or (at your
|
||
option) any later version. See the file COPYING for further details.
|
||
|
||
*/
|
||
|
||
|
||
/** @file function-closure.hpp
|
||
** Partial function application and building a complete function closure.
|
||
** These are features known from functional programming and are here implemented
|
||
** based on std::bind, to support especially the case when some arguments of a
|
||
** function are known at an earlier stage, and should thus be »baked in«, while
|
||
** further arguments will be supplied later, for the actual invocation. This
|
||
** implies to _close_ (and thus bind) some arguments immediately, while keeping
|
||
** other arguments open to — so the result of this operation is again a function,
|
||
** albeit with fewer arguments.
|
||
** Additionally, we allow for _composing_ (chaining) of two functions.
|
||
** @warning this header is in a state of transition as of 6/2025, because functionality
|
||
** of this kind will certainly be needed in future, but with full support for lambdas,
|
||
** move-only types and perfect forwarding. The current implementation of std::bind
|
||
** is already quite optimal regarding this support. A gradual rework has been started,
|
||
** and will lead to a complete rewrite of the core functionality eventually, making
|
||
** better use of variadic templates and library functions like std::apply, which
|
||
** were not available at the time of the first implementation.
|
||
**
|
||
** @todo the implementation is able to handle partial application with N arguments,
|
||
** but currently we need just one argument, thus only this case was wrapped
|
||
** up into a convenient functions func::applyFirst and func::applyLast
|
||
** @todo 11/23 these functor-utils were written at a time when support for handling
|
||
** generic functions in C++ was woefully inadequate; at that time, we neither
|
||
** had Lambda-support in the language, nor the ability to use variadic arguments.
|
||
** Providing a one-shot function-style interface for this kind of manipulations
|
||
** is still considered beneficial, and thus we should gradually modernise
|
||
** the tools we want to retain...
|
||
** @todo 2/25 note that there is a bind_front in C++20 and C++23 will provide a bind_back
|
||
** helper, which would provide the implementation fully in accordance with current
|
||
** expectations (including move, constexpr); if we choose to retain a generic
|
||
** function-style front-end, it should be aligned with these standard facilities.
|
||
** We might want to retain a simple generic interface especially for binding some
|
||
** selected argument, which handles the intricacies of storing the functor.
|
||
** @todo 6/25 note however that the full-fledged partial function application is a
|
||
** **relevant core feature** and is used in the NodeBuilder (see tuple-closure.hpp).
|
||
**
|
||
** @see control::CommandDef usage example
|
||
** @see function-closure-test.hpp
|
||
** @see function-composition-test.hpp
|
||
** @see function.hpp
|
||
**
|
||
*/
|
||
|
||
|
||
#ifndef LIB_META_FUNCTION_CLOSURE_H
|
||
#define LIB_META_FUNCTION_CLOSURE_H
|
||
|
||
#include "lib/meta/function.hpp"
|
||
#include "lib/meta/tuple-helper.hpp"
|
||
#include "lib/util.hpp"
|
||
|
||
#include <functional>
|
||
#include <utility>
|
||
#include <tuple>
|
||
|
||
|
||
|
||
namespace lib {
|
||
namespace meta{
|
||
namespace func{
|
||
|
||
using std::tuple;
|
||
using std::function;
|
||
using std::forward;
|
||
using std::move;
|
||
|
||
|
||
|
||
|
||
namespace { // helpers for binding and applying a function to an argument tuple
|
||
|
||
using std::get;
|
||
|
||
/**
|
||
* this Helper with repetitive specialisations for up to nine arguments
|
||
* is used either to apply a function to arguments given as a tuple, or
|
||
* to create the actual closure (functor) over all function arguments.
|
||
* @todo 2/2025 should be replaced by a single variadic template, and
|
||
* implemented using std::apply. Note also that std::bind would
|
||
* support perfect-forwarding, especially also for the functor;
|
||
* the latter would allow to use move-only functors.
|
||
*/
|
||
template<uint n>
|
||
struct Apply;
|
||
|
||
|
||
template<> //__________________________________
|
||
struct Apply<0> ///< Apply function without Arguments
|
||
{
|
||
template<typename RET, class FUN, class TUP>
|
||
static RET
|
||
bind (FUN& f, TUP&)
|
||
{
|
||
return std::bind (f);
|
||
}
|
||
};
|
||
|
||
|
||
template<> //_________________________________
|
||
struct Apply<1> ///< Apply function with 1 Argument
|
||
{
|
||
template<typename RET, class FUN, class TUP>
|
||
static RET
|
||
bind (FUN& f, TUP & arg)
|
||
{
|
||
return std::bind (f, get<0>(arg));
|
||
}
|
||
};
|
||
|
||
|
||
template<> //_________________________________
|
||
struct Apply<2> ///< Apply function with 2 Arguments
|
||
{
|
||
template<typename RET, class FUN, class TUP>
|
||
static RET
|
||
bind (FUN& f, TUP & arg)
|
||
{
|
||
return std::bind (f, get<0>(arg)
|
||
, get<1>(arg)
|
||
);
|
||
}
|
||
};
|
||
|
||
|
||
template<> //_________________________________
|
||
struct Apply<3> ///< Apply function with 3 Arguments
|
||
{
|
||
template<typename RET, class FUN, class TUP>
|
||
static RET
|
||
bind (FUN& f, TUP & arg)
|
||
{
|
||
return std::bind (f, get<0>(arg)
|
||
, get<1>(arg)
|
||
, get<2>(arg)
|
||
);
|
||
}
|
||
};
|
||
|
||
|
||
template<> //_________________________________
|
||
struct Apply<4> ///< Apply function with 4 Arguments
|
||
{
|
||
template<typename RET, class FUN, class TUP>
|
||
static RET
|
||
bind (FUN& f, TUP & arg)
|
||
{
|
||
return std::bind (f, get<0>(arg)
|
||
, get<1>(arg)
|
||
, get<2>(arg)
|
||
, get<3>(arg)
|
||
);
|
||
}
|
||
};
|
||
|
||
|
||
template<> //_________________________________
|
||
struct Apply<5> ///< Apply function with 5 Arguments
|
||
{
|
||
template<typename RET, class FUN, class TUP>
|
||
static RET
|
||
bind (FUN& f, TUP & arg)
|
||
{
|
||
return std::bind (f, get<0>(arg)
|
||
, get<1>(arg)
|
||
, get<2>(arg)
|
||
, get<3>(arg)
|
||
, get<4>(arg)
|
||
);
|
||
}
|
||
};
|
||
|
||
|
||
template<> //_________________________________
|
||
struct Apply<6> ///< Apply function with 6 Arguments
|
||
{
|
||
template<typename RET, class FUN, class TUP>
|
||
static RET
|
||
bind (FUN& f, TUP & arg)
|
||
{
|
||
return std::bind (f, get<0>(arg)
|
||
, get<1>(arg)
|
||
, get<2>(arg)
|
||
, get<3>(arg)
|
||
, get<4>(arg)
|
||
, get<5>(arg)
|
||
);
|
||
}
|
||
};
|
||
|
||
|
||
template<> //_________________________________
|
||
struct Apply<7> ///< Apply function with 7 Arguments
|
||
{
|
||
template<typename RET, class FUN, class TUP>
|
||
static RET
|
||
bind (FUN& f, TUP & arg)
|
||
{
|
||
return std::bind (f, get<0>(arg)
|
||
, get<1>(arg)
|
||
, get<2>(arg)
|
||
, get<3>(arg)
|
||
, get<4>(arg)
|
||
, get<5>(arg)
|
||
, get<6>(arg)
|
||
);
|
||
}
|
||
};
|
||
|
||
|
||
template<> //_________________________________
|
||
struct Apply<8> ///< Apply function with 8 Arguments
|
||
{
|
||
template<typename RET, class FUN, class TUP>
|
||
static RET
|
||
bind (FUN& f, TUP & arg)
|
||
{
|
||
return std::bind (f, get<0>(arg)
|
||
, get<1>(arg)
|
||
, get<2>(arg)
|
||
, get<3>(arg)
|
||
, get<4>(arg)
|
||
, get<5>(arg)
|
||
, get<6>(arg)
|
||
, get<7>(arg)
|
||
);
|
||
}
|
||
};
|
||
|
||
|
||
template<> //_________________________________
|
||
struct Apply<9> ///< Apply function with 9 Arguments
|
||
{
|
||
template<typename RET, class FUN, class TUP>
|
||
static RET
|
||
bind (FUN& f, TUP & arg)
|
||
{
|
||
return std::bind (f, get<0>(arg)
|
||
, get<1>(arg)
|
||
, get<2>(arg)
|
||
, get<3>(arg)
|
||
, get<4>(arg)
|
||
, get<5>(arg)
|
||
, get<6>(arg)
|
||
, get<7>(arg)
|
||
, get<8>(arg)
|
||
);
|
||
}
|
||
};
|
||
|
||
|
||
|
||
|
||
|
||
|
||
/* ===== Helpers for partial function application ===== */
|
||
|
||
/** @note relying on the implementation type
|
||
* since we need to _build_ placeholders */
|
||
using std::_Placeholder;
|
||
|
||
|
||
/**
|
||
* Build a list of standard function argument placeholder types.
|
||
* For each of the elements of the provided reference list,
|
||
* a Placeholder is added, numbers counting up starting with 1 (!)
|
||
*/
|
||
template<typename TYPES, size_t i=1>
|
||
struct PlaceholderTuple
|
||
: PlaceholderTuple<typename TYPES::List>
|
||
{ };
|
||
|
||
template<typename X, typename TAIL, size_t i>
|
||
struct PlaceholderTuple<Node<X,TAIL>, i>
|
||
{
|
||
using TailPlaceholders = typename PlaceholderTuple<TAIL,i+1>::List;
|
||
|
||
using List = Node<_Placeholder<i>, TailPlaceholders>;
|
||
};
|
||
|
||
template<size_t i>
|
||
struct PlaceholderTuple<Nil, i>
|
||
{
|
||
using List = Nil;
|
||
};
|
||
|
||
|
||
|
||
using std::tuple_element;
|
||
using std::tuple_size;
|
||
using std::get;
|
||
|
||
|
||
/**
|
||
* Builder for a tuple instance, where only some ctor parameters are supplied,
|
||
* while the remaining arguments will be default constructed. The use case is
|
||
* creating of a function binder, where some arguments shall be passed through
|
||
* (and thus be stored in the resulting closure), while other arguments are just
|
||
* marked as "Placeholder" with `std::_Placeholder<i>`.
|
||
* These placeholder marker terms just need to be default constructed, and will
|
||
* then be stored into the desired positions. Later on, when actually invoking
|
||
* such a partially closed function, only the arguments marked with placeholders
|
||
* need to be supplied, while the other arguments will use the values hereby
|
||
* "baked" into the closure.
|
||
* @tparam TAR full target tuple type. Some oft the elements within this tuple will
|
||
* be default constructed, some will be initialised from the SRC tuple
|
||
* @tparam SRC argument tuple type, for the values _actually to be initialised_ here.
|
||
* @tparam start position within \a SRC, at which the sequence of init-arguments starts;
|
||
* all other positions will just be default initialised
|
||
* @see lib::meta::TupleConstructor
|
||
*/
|
||
template<typename SRC, typename TAR, size_t start>
|
||
struct PartiallyInitTuple
|
||
{
|
||
template<size_t i>
|
||
using DestType = typename std::tuple_element<i, TAR>::type;
|
||
|
||
|
||
/**
|
||
* define those index positions in the target tuple,
|
||
* where init arguments shall be used on construction.
|
||
* All other arguments will just be default initialised.
|
||
*/
|
||
static constexpr bool
|
||
useArg (size_t idx)
|
||
{
|
||
return (start <= idx)
|
||
and (idx < start + std::tuple_size<SRC>());
|
||
}
|
||
|
||
|
||
|
||
template<size_t idx, bool doPick = PartiallyInitTuple::useArg(idx)>
|
||
struct IndexMapper
|
||
{
|
||
SRC const& initArgs;
|
||
|
||
operator DestType<idx>()
|
||
{
|
||
return std::get<idx-start> (initArgs);
|
||
}
|
||
};
|
||
|
||
template<size_t idx>
|
||
struct IndexMapper<idx, false>
|
||
{
|
||
SRC const& initArgs;
|
||
|
||
operator DestType<idx>()
|
||
{
|
||
return DestType<idx>();
|
||
}
|
||
};
|
||
};
|
||
|
||
} // (END) impl-namespace
|
||
|
||
|
||
|
||
|
||
/* ======= core operations: closures and partial application ========= */
|
||
|
||
/**
|
||
* Closure-creating template.
|
||
* The instance is linked (reference) to a given concrete argument tuple.
|
||
* A functor with a matching signature may then either be _closed_ over
|
||
* this argument values, or even be invoked right away with theses arguments.
|
||
* @warning we take functor objects _and parameters_ by reference
|
||
*/
|
||
template<typename SIG>
|
||
class TupleApplicator
|
||
{
|
||
using Args = typename _Fun<SIG>::Args;
|
||
using Ret = typename _Fun<SIG>::Ret;
|
||
|
||
using BoundFunc = function<Ret()>;
|
||
|
||
enum { ARG_CNT = count<typename Args::List>() };
|
||
|
||
|
||
/** storing a ref to the parameter tuple */
|
||
Tuple<Args>& params_;
|
||
|
||
public:
|
||
TupleApplicator (Tuple<Args>& args)
|
||
: params_(args)
|
||
{ }
|
||
|
||
BoundFunc bind (SIG& f) { return Apply<ARG_CNT>::template bind<BoundFunc> (f, params_); }
|
||
BoundFunc bind (function<SIG> const& f) { return Apply<ARG_CNT>::template bind<BoundFunc> (f, params_); }
|
||
|
||
template<class FUN>
|
||
Ret
|
||
operator() (FUN&& f)
|
||
{
|
||
ASSERT_VALID_SIGNATURE (FUN,SIG);
|
||
return std::apply (forward<FUN> (f), params_);
|
||
}
|
||
};
|
||
|
||
|
||
template<class FUN, class TUP, typename = enable_if_Tuple<TUP>>
|
||
auto
|
||
bindArgTuple (FUN&& fun, TUP&& tuple)
|
||
{
|
||
return std::apply ([functor = forward<FUN>(fun)]
|
||
(auto&&... args)
|
||
{
|
||
return std::bind (move(functor)
|
||
,forward<decltype(args)> (args) ...);
|
||
}
|
||
,std::forward<TUP> (tuple));
|
||
}
|
||
|
||
|
||
|
||
/**
|
||
* Closing a function over its arguments.
|
||
* This is a small usage example or spin-off,
|
||
* having almost the same effect than invoking `std::bind()`.
|
||
* The notable difference is that the function arguments for
|
||
* creating the closure are passed in as one tuple compound.
|
||
*/
|
||
template<typename SIG>
|
||
class FunctionClosure
|
||
{
|
||
typedef typename _Fun<SIG>::Args Args;
|
||
typedef typename _Fun<SIG>::Ret Ret;
|
||
|
||
function<Ret(void)> closure_;
|
||
|
||
public:
|
||
FunctionClosure (SIG& f, Tuple<Args>& args)
|
||
: closure_{bindArgTuple (f, args)}
|
||
{ }
|
||
FunctionClosure (function<SIG> const& f, Tuple<Args>& args)
|
||
: closure_{bindArgTuple (f, args)}
|
||
{ }
|
||
|
||
Ret operator() () { return closure_(); }
|
||
|
||
typedef Ret result_type; ///< for STL use
|
||
typedef void argument_type;
|
||
};
|
||
|
||
|
||
|
||
|
||
/**
|
||
* Partial function application
|
||
* Takes a function and a value tuple,
|
||
* using the latter to close function arguments
|
||
* either from the front (left) or aligned to the end
|
||
* of the function argument list. Result is a "reduced" function,
|
||
* expecting only the remaining "un-closed" arguments at invocation.
|
||
* @tparam SIG signature of the function to be closed, either as
|
||
* function reference type or `std::function` object
|
||
* @tparam VAL type sequence describing the tuple of values
|
||
* used for closing arguments
|
||
* @note the construction of this helper template does not verify or
|
||
* match types to the signature. In case of mismatch, you'll get
|
||
* a compilation failure from `std::bind` (which can be confusing)
|
||
* @todo 11/2023 started with modernising these functor utils.
|
||
* The most relevant bindFirst() / bindLast() operations do no longer
|
||
* rely on the PApply template. There is however the more general case
|
||
* of _binding multiple arguments,_ which is still used at a few places.
|
||
* Possibly PApply should be rewritten from scratch, using modern tooling.
|
||
*/
|
||
template<typename SIG, typename VAL>
|
||
class PApply
|
||
{
|
||
using Args = typename _Fun<SIG>::Args;
|
||
using Ret = typename _Fun<SIG>::Ret;
|
||
using ArgsList = typename Args::List;
|
||
using ValList = typename VAL::List;
|
||
using ValTypes = typename TySeq<ValList>::Seq; // reconstruct a type-seq from a type-list
|
||
|
||
enum { ARG_CNT = count<ArgsList>()
|
||
, VAL_CNT = count<ValList>()
|
||
, ROFFSET = (VAL_CNT < ARG_CNT)? ARG_CNT-VAL_CNT : 0
|
||
};
|
||
|
||
|
||
// create list of the *remaining* arguments, after applying the ValList
|
||
using LeftReduced = typename Splice<ArgsList, ValList>::Back;
|
||
using RightReduced = typename Splice<ArgsList, ValList, ROFFSET>::Front;
|
||
|
||
using ArgsL = typename TySeq<LeftReduced>::Seq;
|
||
using ArgsR = typename TySeq<RightReduced>::Seq;
|
||
|
||
|
||
// build a list, where each of the *remaining* arguments is replaced by a placeholder marker
|
||
using TrailingPlaceholders = typename func::PlaceholderTuple<LeftReduced>::List;
|
||
using LeadingPlaceholders = typename func::PlaceholderTuple<RightReduced>::List;
|
||
|
||
// ... and splice these placeholders on top of the original argument type list,
|
||
// thus retaining the types to be closed, but setting a placeholder for each remaining argument
|
||
using LeftReplaced = typename Splice<ArgsList, TrailingPlaceholders, VAL_CNT>::List;
|
||
using RightReplaced = typename Splice<ArgsList, LeadingPlaceholders, 0 >::List;
|
||
|
||
using LeftReplacedTypes = typename TySeq<LeftReplaced>::Seq;
|
||
using RightReplacedTypes = typename TySeq<RightReplaced>::Seq;
|
||
|
||
// create a "builder" helper, which accepts exactly the value tuple elements
|
||
// and puts them at the right location, while default-constructing the remaining
|
||
// (=placeholder)-arguments. Using this builder helper, we can finally set up
|
||
// the argument tuples (Left/RightReplacedArgs) used for the std::bind call
|
||
template<class SRC, class TAR, size_t i>
|
||
using IdxSelectorL = typename PartiallyInitTuple<SRC, TAR, 0>::template IndexMapper<i>;
|
||
|
||
template<class SRC, class TAR, size_t i>
|
||
using IdxSelectorR = typename PartiallyInitTuple<SRC, TAR, ROFFSET>::template IndexMapper<i>;
|
||
|
||
using BuildL = TupleConstructor<LeftReplacedTypes, IdxSelectorL>;
|
||
using BuildR = TupleConstructor<RightReplacedTypes, IdxSelectorR>;
|
||
|
||
|
||
/** Tuple to hold all argument values, starting from left.
|
||
* Any remaining positions behind the substitute values are occupied by binding placeholders */
|
||
using LeftReplacedArgs = Tuple<LeftReplacedTypes>;
|
||
|
||
/** Tuple to hold all argument values, aligned to the end of the function argument list.
|
||
* Any remaining positions before the substitute values are occupied by binding placeholders */
|
||
using RightReplacedArgs = Tuple<RightReplacedTypes>;
|
||
|
||
|
||
public:
|
||
using LeftReducedFunc = function<typename BuildFunType<Ret,ArgsL>::Sig>;
|
||
using RightReducedFunc = function<typename BuildFunType<Ret,ArgsR>::Sig>;
|
||
|
||
|
||
/** do a partial function application, closing the first arguments<br/>
|
||
* `f(a,b,c)->res + (a,b)` yields `f(c)->res`
|
||
*
|
||
* @param f function, function pointer or functor
|
||
* @param arg value tuple, used to close function arguments starting from left
|
||
* @return new function object, holding copies of the values and using them at the
|
||
* closed arguments; on invocation, only the remaining arguments need to be supplied.
|
||
* @note BuildL, and consequently std::bind _must take the arguments by-value._ Any attempt
|
||
* towards »perfect-forwarding« would be potentially fragile and not worth the effort,
|
||
* since the optimiser sees the operation as a whole.
|
||
* @todo 2/2025 However, the LeftReplacedArgs _could_ then possibly moved into the bind function,
|
||
* as could the functor, once we replace the Apply-template by STDLIB features.
|
||
* @todo 5/2025 seems indeed we could perfect-forward everything into the binder object.
|
||
*/
|
||
static LeftReducedFunc
|
||
bindFront (SIG const& f, Tuple<ValTypes> arg)
|
||
{
|
||
LeftReplacedArgs params {BuildL(std::move(arg))};
|
||
return bindArgTuple (f, params);
|
||
}
|
||
|
||
/** do a partial function application, closing the last arguments<br/>
|
||
* `f(a,b,c)->res + (b,c)` yields `f(a)->res`
|
||
*
|
||
* @param f function, function pointer or functor
|
||
* @param arg value tuple, used to close function arguments, aligned to the right end.
|
||
* @return new function object, holding copies of the values and using them at the
|
||
* closed arguments; on invocation, only the remaining arguments need to be supplied.
|
||
*/
|
||
static RightReducedFunc
|
||
bindBack (SIG const& f, Tuple<ValTypes> arg)
|
||
{
|
||
RightReplacedArgs params {BuildR(std::move(arg))};
|
||
return bindArgTuple (f, params);
|
||
}
|
||
};
|
||
|
||
|
||
|
||
/**
|
||
* Bind a specific argument to an arbitrary value.
|
||
* Notably this "value" might be another binder.
|
||
*/
|
||
template<typename SIG, typename X, uint pos>
|
||
class BindToArgument
|
||
{
|
||
using Args = typename _Fun<SIG>::Args;
|
||
using Ret = typename _Fun<SIG>::Ret;
|
||
using ArgsList = typename Args::List;
|
||
using ValList = typename TySeq<X>::List;
|
||
|
||
enum { ARG_CNT = count<ArgsList>() };
|
||
|
||
using RemainingFront = typename Splice<ArgsList, ValList, pos>::Front;
|
||
using RemainingBack = typename Splice<ArgsList, ValList, pos>::Back;
|
||
using PlaceholdersBefore = typename func::PlaceholderTuple<RemainingFront>::List;
|
||
using PlaceholdersBehind = typename func::PlaceholderTuple<RemainingBack,pos+1>::List;
|
||
|
||
using PreparedArgsRaw = typename Append<typename Append<PlaceholdersBefore // arguments before the splice: passed-through
|
||
,ValList >::List // splice in the value tuple
|
||
,PlaceholdersBehind // arguments behind the splice: passed-through
|
||
>::List;
|
||
using PreparedArgs = Prefix<PreparedArgsRaw, ARG_CNT>;
|
||
using ReducedArgs = typename Append<RemainingFront, RemainingBack>::List;
|
||
|
||
using PreparedArgTypes = typename TySeq<PreparedArgs>::Seq;
|
||
using RemainingArgs = typename TySeq<ReducedArgs>::Seq;
|
||
|
||
using ReducedSig = typename BuildFunType<Ret,RemainingArgs>::Sig;
|
||
|
||
template<class SRC, class TAR, size_t i>
|
||
using IdxSelector = typename PartiallyInitTuple<SRC, TAR, pos>::template IndexMapper<i>;
|
||
|
||
using BuildPreparedArgs = TupleConstructor<PreparedArgTypes, IdxSelector>;
|
||
|
||
|
||
|
||
public:
|
||
using ReducedFunc = function<ReducedSig>;
|
||
|
||
static ReducedFunc
|
||
reduced (SIG& f, X val)
|
||
{
|
||
Tuple<PreparedArgTypes> params {BuildPreparedArgs{std::make_tuple (val)}};
|
||
return bindArgTuple (f, params);
|
||
}
|
||
};
|
||
|
||
|
||
|
||
namespace { // ...helpers for specifying types in function declarations....
|
||
|
||
using std::get;
|
||
using util::unConst;
|
||
|
||
|
||
template<typename SIG, typename ARG>
|
||
struct _Clo
|
||
{
|
||
using Ret = typename _Fun<SIG>::Ret;
|
||
using Signature = typename BuildFunType<Ret, ARG>::Sig;
|
||
using Type = FunctionClosure<Signature>;
|
||
};
|
||
|
||
template<typename FUN1, typename FUN2>
|
||
struct _Chain
|
||
{
|
||
using Ret = typename _Fun<FUN2>::Ret;
|
||
using Args = typename _Fun<FUN1>::Args;
|
||
|
||
using FunType = typename BuildFunType<Ret,Args>::Fun;
|
||
static auto adaptedFunType() { return FunType{}; }
|
||
|
||
|
||
template<typename F1, typename F2
|
||
,typename RET, typename... ARGS>
|
||
static auto
|
||
composedFunctions (F1&& f1, F2&& f2, _Fun<RET(ARGS...)>)
|
||
{
|
||
tuple<F1,F2> binding{forward<F1> (f1)
|
||
,forward<F2> (f2)
|
||
};
|
||
return [binding = move(binding)]
|
||
(ARGS ...args) -> RET
|
||
{
|
||
auto& functor1 = get<0>(binding);
|
||
auto& functor2 = get<1>(binding);
|
||
//
|
||
return functor2 (functor1 (forward<ARGS> (args)...));
|
||
};
|
||
}
|
||
};
|
||
|
||
template<typename FUN>
|
||
struct _PapS
|
||
{
|
||
using Ret = typename _Fun<FUN>::Ret;
|
||
using Args = typename _Fun<FUN>::Args;
|
||
using Arg = typename Split<Args>::Head;
|
||
using Rest = typename Split<Args>::Tail;
|
||
|
||
using FunType = typename BuildFunType<Ret,Rest>::Fun;
|
||
static auto adaptedFunType() { return FunType{}; }
|
||
|
||
|
||
template<typename F, typename A
|
||
,typename RET, typename... ARGS>
|
||
static auto
|
||
bindFrontArg (F&& fun, A&& arg, _Fun<RET(ARGS...)>)
|
||
{
|
||
tuple<F,A> binding{forward<F> (fun)
|
||
,forward<A> (arg)
|
||
};
|
||
return [binding = move(binding)]
|
||
(ARGS ...args) -> RET
|
||
{
|
||
auto& functor = get<0>(binding);
|
||
// //Warning: might corrupt ownership
|
||
return functor ( forward<A> (unConst (get<1>(binding)))
|
||
, forward<ARGS> (args)...);
|
||
};
|
||
}
|
||
};
|
||
|
||
template<typename FUN>
|
||
struct _PapE
|
||
{
|
||
using Ret = typename _Fun<FUN>::Ret;
|
||
using Args = typename _Fun<FUN>::Args;
|
||
using Arg = typename Split<Args>::End;
|
||
using Rest = typename Split<Args>::Prefix;
|
||
|
||
using FunType = typename BuildFunType<Ret,Rest>::Fun;
|
||
static auto adaptedFunType() { return FunType{}; }
|
||
|
||
|
||
template<typename F, typename A
|
||
,typename RET, typename... ARGS>
|
||
static auto
|
||
bindBackArg (F&& fun, A&& arg, _Fun<RET(ARGS...)>)
|
||
{
|
||
tuple<F,A> binding{forward<F> (fun)
|
||
,forward<A> (arg)
|
||
};
|
||
return [binding = move(binding)]
|
||
(ARGS ...args) -> RET
|
||
{
|
||
auto& functor = get<0>(binding);
|
||
//
|
||
return functor ( forward<ARGS> (args)...
|
||
, forward<A> (unConst (get<1>(binding))));
|
||
};
|
||
}
|
||
};
|
||
|
||
} // (End) argument type shortcuts
|
||
|
||
|
||
|
||
|
||
/* ========== function-style interface ============= */
|
||
|
||
/** close the given function over all arguments,
|
||
* using the values from the argument tuple.
|
||
* @return a closure object, which can be
|
||
* invoked later to yield the
|
||
* function result. */
|
||
template<typename SIG, typename...ARG>
|
||
inline
|
||
typename _Clo<SIG,TySeq<ARG...>>::Type
|
||
closure (SIG& f, std::tuple<ARG...>& args)
|
||
{
|
||
using Closure = typename _Clo<SIG,TySeq<ARG...>>::Type;
|
||
return Closure (f,args);
|
||
}
|
||
|
||
|
||
/** close the given function over the first argument.
|
||
* @warning never tie an ownership-managing object by-value! */
|
||
template<typename FUN, typename ARG>
|
||
inline auto
|
||
applyFirst (FUN&& fun, ARG&& arg)
|
||
{
|
||
static_assert (_Fun<FUN>(), "expect something function-like");
|
||
return _PapS<FUN>::bindFrontArg (forward<FUN> (fun)
|
||
,forward<ARG> (arg)
|
||
,_PapS<FUN>::adaptedFunType());
|
||
}
|
||
|
||
/** close the given function over the last argument */
|
||
template<typename FUN, typename ARG>
|
||
inline auto
|
||
applyLast (FUN&& fun, ARG&& arg)
|
||
{
|
||
static_assert (_Fun<FUN>(), "expect something function-like");
|
||
return _PapE<FUN>::bindBackArg (forward<FUN> (fun)
|
||
,forward<ARG> (arg)
|
||
,_PapE<FUN>::adaptedFunType());
|
||
}
|
||
|
||
|
||
/** bind the last function argument to an arbitrary term,
|
||
* which especially might be a (nested) binder... */
|
||
template<typename SIG, typename TERM>
|
||
inline
|
||
typename _PapE<SIG>::FunType::Functor
|
||
bindLast (SIG& f, TERM&& arg)
|
||
{
|
||
enum { LAST_POS = -1 + count<typename _Fun<SIG>::Args>() };
|
||
return BindToArgument<SIG,TERM,LAST_POS>::reduced (f, std::forward<TERM> (arg));
|
||
}
|
||
|
||
|
||
/** build a functor chaining the given functions: feed the result of f1 into f2.
|
||
* @note the mathematical notation would be `chained ≔ f2 ∘f1`
|
||
*/
|
||
template<typename FUN1, typename FUN2>
|
||
inline auto
|
||
chained (FUN1&& f1, FUN2&& f2)
|
||
{
|
||
static_assert (_Fun<FUN1>(), "expect something function-like for function-1");
|
||
static_assert (_Fun<FUN2>(), "expect something function-like for function-2");
|
||
using Chain = _Chain<FUN1,FUN2>;
|
||
return Chain::composedFunctions (forward<FUN1> (f1)
|
||
,forward<FUN2> (f2)
|
||
,Chain::adaptedFunType());
|
||
}
|
||
|
||
|
||
|
||
}}} // namespace lib::meta::func
|
||
#endif
|