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#ifndef BOOST_CONTRACT_CALL_IF_HPP_
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#define BOOST_CONTRACT_CALL_IF_HPP_
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// Copyright (C) 2008-2018 Lorenzo Caminiti
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// Distributed under the Boost Software License, Version 1.0 (see accompanying
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// file LICENSE_1_0.txt or a copy at http://www.boost.org/LICENSE_1_0.txt).
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// See: http://www.boost.org/doc/libs/release/libs/contract/doc/html/index.html
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/** @file
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Statically disable compilation and execution of functor calls.
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@note These facilities allow to emulate C++17 <c>if constexpr</c> statements
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when used together with functor templates (and C++14 generic lambdas).
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Therefore, they are not useful on C++17 compilers where
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<c> if constexpr</c> can be directly used instead.
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*/
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#include <boost/contract/detail/none.hpp>
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#include <boost/make_shared.hpp>
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#include <boost/shared_ptr.hpp>
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#include <boost/utility/enable_if.hpp>
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#include <boost/config.hpp>
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/* PRIVATE */
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/** @cond */
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// Boost.ResultOf not always able to deduce lambda result type (on MSVC).
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#ifndef BOOST_NO_CXX11_DECLTYPE
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#include <boost/utility/declval.hpp>
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#define BOOST_CONTRACT_CALL_IF_RESULT_OF_(F) \
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decltype(boost::declval<F>()())
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#else
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#include <boost/utility/result_of.hpp>
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#define BOOST_CONTRACT_CALL_IF_RESULT_OF_(F) \
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typename boost::result_of<F()>::type
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#endif
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/** @endcond */
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/* CODE */
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namespace boost { namespace contract {
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/**
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Select compilation and execution of functor template calls using a static
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boolean predicate (not needed on C++17 compilers, use <c>if constexpr</c>
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instead).
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This class template has no members because it is never used directly, it is only
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used via its specializations.
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Usually this class template is instantiated only via the return value of
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@RefFunc{boost::contract::call_if} and @RefFunc{boost::contract::call_if_c}.
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@see @RefSect{extras.assertion_requirements__templates_,
|
Assertion Requirements}
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@tparam Pred Static boolean predicate that selects which functor template
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call to compile and execute.
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@tparam Then Type of the functor template to call if the static predicate
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@c Pred is @c true.
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@tparam ThenResult Return type of then-branch functor template call (this is
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usually automatically deduced by this library so it is never explicitly
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specified by the user, and that is why it is often marked as
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@c internal_type in this documentation).
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*/
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template<bool Pred, typename Then, typename ThenResult =
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#ifndef BOOST_CONTRACT_DETAIL_DOXYGEN
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boost::contract::detail::none
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#else
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internal_type
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#endif
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>
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struct call_if_statement {}; // Empty so cannot be used (but copyable).
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/**
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Template specialization to dispatch between then-branch functor template calls
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that return void and the ones that return non-void (not needed on C++17
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compilers, use <c>if constexpr</c> instead).
|
|
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The base class is a call-if statement so the else and else-if statements can be
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specified if needed.
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Usually this class template is instantiated only via the return value of
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@RefFunc{boost::contract::call_if} and @RefFunc{boost::contract::call_if_c}.
|
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@note The <c>result_of<Then()>::type</c> expression needs be evaluated only
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when the static predicate is already checked to be @c true (because
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@c Then() is required to compile only in that case).
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Thus, this template specialization introduces an extra level of
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indirection necessary for proper lazy evaluation of this result-of
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expression.
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@see @RefSect{extras.assertion_requirements__templates_,
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Assertion Requirements}
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@tparam Then Type of functor template to call when the static predicate is
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@c true (as it is for this template specialization).
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*/
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template<typename Then>
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struct call_if_statement<true, Then,
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#ifndef BOOST_CONTRACT_DETAIL_DOXYGEN
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boost::contract::detail::none
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#else
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internal_type
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#endif
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> :
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call_if_statement<true, Then,
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#ifndef BOOST_CONTRACT_DETAIL_DOXYGEN
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BOOST_CONTRACT_CALL_IF_RESULT_OF_(Then)
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#else
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typename result_of<Then()>::type
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#endif
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>
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{ // Copyable (as its base).
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/**
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Construct this object with the then-branch functor template.
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@param f Then-branch nullary functor template.
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The functor template call @c f() is compiled and called for this
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template specialization (because the if-statement static
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predicate is @c true).
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The return type of @c f() must be the same as (or implicitly
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convertible to) the return type of all other functor template
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calls specified for this call-if object.
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*/
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explicit call_if_statement(Then f) : call_if_statement<true, Then,
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BOOST_CONTRACT_CALL_IF_RESULT_OF_(Then)>(f) {}
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};
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/**
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Template specialization to handle static predicates that are @c true for
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then-branch functor template calls that do not return void (not needed on C++17
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compilers, use <c>if constexpr</c> instead).
|
|
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Usually this class template is instantiated only via the return value of
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@RefFunc{boost::contract::call_if} and @RefFunc{boost::contract::call_if_c}.
|
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@see @RefSect{extras.assertion_requirements__templates_,
|
Assertion Requirements}
|
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@tparam Then Type of functor template to call when the static predicate is
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@c true (as it is for this template specialization).
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@tparam ThenResult Non-void return type of the then-branch functor template
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call.
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*/
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template<typename Then, typename ThenResult>
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struct call_if_statement<true, Then, ThenResult> { // Copyable (as *).
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/**
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Construct this object with the then-branch functor template.
|
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@param f Then-branch nullary functor template.
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The functor template call @c f() is actually compiled and
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executed for this template specialization (because the
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if-statement static predicate is @c true).
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The return type of @c f() must be the same as (or implicitly
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convertible to) the @p ThenResult type.
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*/
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explicit call_if_statement(Then f) :
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r_(boost::make_shared<ThenResult>(f())) {}
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/**
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This implicit type conversion returns a copy of the value returned by the
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call to the then-branch functor template.
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*/
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operator ThenResult() const { return *r_; }
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/**
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Specify the else-branch functor template.
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@param f Else-branch nullary functor template.
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The functor template call @c f() is never compiled or executed
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for this template specialization (because the if-statement
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static predicate is @c true).
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The return type of @c f() must be the same as (or implicitly
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convertible to) the @p ThenResult type.
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@return A copy of the value returned by the call to the then-branch functor
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template (because the else-branch functor template call is not
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executed).
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*/
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template<typename Else>
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ThenResult else_(Else const&
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#ifdef BOOST_CONTRACT_DETAIL_DOXYGEN
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f
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#endif
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) const { return *r_; }
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/**
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Specify an else-if-branch functor template (using a static boolean
|
predicate).
|
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@param f Else-if-branch nullary functor template.
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The functor template call @c f() is never compiled or executed
|
for this template specialization (because the if-statement
|
static predicate is @c true).
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The return type of @c f() must be the same as (or implicitly
|
convertible to) the @p ThenResult type.
|
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@tparam ElseIfPred Static boolean predicate selecting which functor
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template call to compile and execute.
|
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@return A call-if statement so the else statement and additional else-if
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statements can be specified if needed.
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Eventually, it will be the return value of the then-branch functor
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template call for this template specialization (because the
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if-statement static predicate is @c true).
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*/
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template<bool ElseIfPred, typename ElseIfThen>
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call_if_statement<true, Then, ThenResult> else_if_c(
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ElseIfThen const&
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#ifdef BOOST_CONTRACT_DETAIL_DOXYGEN // Avoid unused param warning.
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f
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#endif
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) const { return *this; }
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/**
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Specify an else-if-branch functor template (using a nullary boolean
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meta-function).
|
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@param f Else-if-branch nullary functor template.
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The functor template call @c f() is never compiled or executed
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for this template specialization (because the if-statement
|
static predicate is @c true).
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The return type of @c f() must be the same as (or implicitly
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convertible to) the @p ThenResult type.
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@tparam ElseIfPred Nullary boolean meta-function selecting which functor
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template call to compile and execute.
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@return A call-if statement so the else statement and additional else-if
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statements can be specified if needed.
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Eventually, it will be the return value of the then-branch functor
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template call for this template specialization (because the
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if-statement static predicate is @c true).
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*/
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template<class ElseIfPred, typename ElseIfThen>
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call_if_statement<true, Then, ThenResult> else_if(
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ElseIfThen const&
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#ifdef BOOST_CONTRACT_DETAIL_DOXYGEN // Avoid unused param warning.
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f
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#endif
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) const { return *this; }
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private:
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boost::shared_ptr<ThenResult> r_;
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};
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/**
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Template specialization to handle static predicates that are @c true for
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then-branch functor template calls that return void (not needed on C++17
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compilers, use <c>if constexpr</c> instead).
|
|
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Usually this class template is instantiated only via the return value of
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@RefFunc{boost::contract::call_if} and @RefFunc{boost::contract::call_if_c}.
|
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@see @RefSect{extras.assertion_requirements__templates_,
|
Assertion Requirements}
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@tparam Then Type of functor template to call when the static predicate if
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@c true (as it is for this template specialization).
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*/
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template<typename Then>
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struct call_if_statement<true, Then, void> { // Copyable (no data).
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/**
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Construct this object with the then-branch functor template.
|
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@param f Then-branch nullary functor template.
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The functor template call @c f() is actually compiled and
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executed for this template specialization (because the
|
if-statement static predicate is @c true).
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The return type of @c f() must be @c void for this template
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specialization (because the then-branch functor template calls
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return void).
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*/
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explicit call_if_statement(Then f) { f(); }
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// Cannot provide `operator ThenResult()` here, because ThenResult is void.
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/**
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Specify the else-branch functor template.
|
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@param f Else-branch nullary functor template.
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The functor template call @c f() is never compiled or executed
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for this template specialization (because the if-statement
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static predicate is @c true).
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The return type of @c f() must be @c void for this template
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specialization (because the then-branch functor template calls
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return void).
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*/
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template<typename Else>
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void else_(Else const&
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#ifdef BOOST_CONTRACT_DETAIL_DOXYGEN
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f
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#endif
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) const {}
|
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/**
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Specify an else-if-branch functor template (using a static boolean
|
predicate).
|
|
@param f Else-if-branch nullary functor template.
|
The functor template call @c f() is never compiled or executed
|
for this template specialization (because the if-statement
|
static predicate is @c true).
|
The return type of @c f() must be @c void for this template
|
specialization (because the then-branch functor template calls
|
return void).
|
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@tparam ElseIfPred Static boolean predicate selecting which functor
|
template call to compile and execute.
|
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@return A call-if statement so the else statement and additional else-if
|
statements can be specified if needed.
|
Eventually, it will return void for this template specialization
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(because the then-branch functor template calls return void).
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*/
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template<bool ElseIfPred, typename ElseIfThen>
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call_if_statement<true, Then, void> else_if_c(
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ElseIfThen const&
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#ifdef BOOST_CONTRACT_DETAIL_DOXYGEN // Avoid unused param warning.
|
f
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#endif
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) const { return *this; }
|
|
/**
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Specify an else-if-branch functor template (using a nullary boolean
|
meta-function).
|
|
@param f Else-if-branch nullary functor template.
|
The functor template call @c f() is never compiled or executed
|
for this template specialization (because the if-statement
|
static predicate is @c true).
|
The return type of @c f() must be @c void for this template
|
specialization (because the then-branch functor template calls
|
return void).
|
|
@tparam ElseIfPred Nullary boolean meta-function selecting which functor
|
template call to compile and execute.
|
|
@return A call-if statement so the else statement and additional else-if
|
statements can be specified if needed.
|
Eventually, it will return void for this template specialization
|
(because the then-branch functor template calls return void).
|
*/
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template<class ElseIfPred, typename ElseIfThen>
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call_if_statement<true, Then, void> else_if(
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ElseIfThen const&
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#ifdef BOOST_CONTRACT_DETAIL_DOXYGEN // Avoid unused param warning.
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f
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#endif
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) const { return *this; }
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};
|
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/**
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Template specialization to handle static predicates that are @c false (not
|
needed on C++17 compilers, use <c>if constexpr</c> instead).
|
|
This template specialization handles all else-branch functor template calls
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(whether they return void or not).
|
Usually this class template is instantiated only via the return value of
|
@RefFunc{boost::contract::call_if} and @RefFunc{boost::contract::call_if_c}.
|
|
@see @RefSect{extras.assertion_requirements__templates_,
|
Assertion Requirements}
|
|
@tparam Then Type of functor template to call when the static predicate is
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@c true (never the case for this template specialization).
|
*/
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template<typename Then> // Copyable (no data).
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struct call_if_statement<false, Then,
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#ifndef BOOST_CONTRACT_DETAIL_DOXYGEN
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boost::contract::detail::none
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#else
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internal_type
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#endif
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> {
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/**
|
Construct this object with the then-branch functor template.
|
|
@param f Then-branch nullary functor template.
|
The functor template call @c f() is never compiled or executed
|
for this template specialization (because the if-statement
|
static predicate is @c false).
|
The return type of @c f() must be the same as (or implicitly
|
convertible to) the return type of all other functor template
|
calls specified for this call-if object.
|
*/
|
explicit call_if_statement(Then const&
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#ifdef BOOST_CONTRACT_DETAIL_DOXYGEN
|
f
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#endif
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) {}
|
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// Do not provide `operator result_type()` here, require else_ instead.
|
|
/**
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Specify the else-branch functor template.
|
|
@note The <c>result_of<Else()>::type</c> expression needs be evaluated
|
only when the static predicate is already checked to be @c false
|
(because @c Else() is required to compile only in that case).
|
Thus, this result-of expression is evaluated lazily and only in
|
instantiations of this template specialization.
|
|
@param f Else-branch nullary functor template.
|
The functor template call @c f() is actually compiled and
|
executed for this template specialization (because the
|
if-statement static predicate is @c false).
|
The return type of @c f() must be the same as (or implicitly
|
convertible to) the return type of all other functor template
|
calls specified for this call-if object.
|
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@return A copy of the value returned by the call to the else-branch functor
|
template @c f().
|
*/
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template<typename Else>
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#ifndef BOOST_CONTRACT_DETAIL_DOXYGEN
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BOOST_CONTRACT_CALL_IF_RESULT_OF_(Else)
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#else
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typename result_of<Else()>::type
|
#endif
|
else_(Else f) const { return f(); }
|
|
/**
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Specify an else-if-branch functor template (using a static boolean
|
predicate).
|
|
@param f Else-if-branch nullary functor template.
|
The functor template call @c f() is actually compiled and
|
executed if and only if @c ElseIfPred is @c true (because the
|
if-statement static predicate is already @c false for this
|
template specialization).
|
The return type of @c f() must be the same as (or implicitly
|
convertible to) the return type of all other functor template
|
calls specified for this call-if object.
|
|
@tparam ElseIfPred Static boolean predicate selecting which functor
|
template call to compile and execute.
|
|
@return A call-if statement so the else statement and additional else-if
|
statements can be specified if needed.
|
Eventually, this will be the return value of the one functor
|
template call being compiled and executed.
|
*/
|
template<bool ElseIfPred, typename ElseIfThen>
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call_if_statement<ElseIfPred, ElseIfThen> else_if_c(ElseIfThen f) const {
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return call_if_statement<ElseIfPred, ElseIfThen>(f);
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}
|
|
/**
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Specify an else-if-branch functor template (using a nullary boolen
|
meta-function).
|
|
@param f Else-if-branch nullary functor template.
|
The functor template call @c f() is actually compiled and
|
executed if and only if @c ElseIfPred::value is @c true (because
|
the if-statement static predicate is already @c false for this
|
template specialization).
|
The return type of @c f() must be the same as (or implicitly
|
convertible to) the return type of all other functor template
|
calls specified for this call-if object.
|
|
@tparam ElseIfPred Nullary boolean meta-function selecting which functor
|
template call to compile and execute.
|
|
@return A call-if statement so the else statement and additional else-if
|
statements can be specified if needed.
|
Eventually, this will be the return value of the one functor
|
template call being compiled and executed.
|
*/
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template<class ElseIfPred, typename ElseIfThen>
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call_if_statement<ElseIfPred::value, ElseIfThen> else_if(ElseIfThen f)
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const {
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return call_if_statement<ElseIfPred::value, ElseIfThen>(f);
|
}
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};
|
|
/**
|
Select compilation and execution of functor template calls using a static
|
boolean predicate (not needed on C++17 compilers, use <c>if constexpr</c>
|
instead).
|
|
Create a call-if object with the specified then-branch functor template:
|
|
@code
|
boost::contract::call_if_c<Pred1>(
|
then_functor_template1
|
).template else_if_c<Pred2>( // Optional.
|
then_functor_template2
|
) // Optionally, other `else_if_c` or
|
... // `else_if`.
|
.else_( // Optional for `void` functors,
|
else_functor_template // but required for non `void`.
|
)
|
@endcode
|
|
Optional functor templates for else-if-branches and the else-branch can be
|
specified as needed (the else-branch function template is required if @c f
|
returns non-void).
|
|
@see @RefSect{extras.assertion_requirements__templates_,
|
Assertion Requirements}
|
|
@param f Then-branch nullary functor template.
|
The functor template call @c f() is compiled and executed if and
|
only if @c Pred is @c true.
|
The return type of other functor template calls specified for this
|
call-if statement (else-branch, else-if-branches, etc.) must be the
|
same as (or implicitly convertible to) the return type of
|
then-branch functor call @c f().
|
|
@tparam Pred Static boolean predicate selecting which functor template call
|
to compile and execute.
|
|
@return A call-if statement so else and else-if statements can be specified if
|
needed.
|
Eventually, this will be the return value of the one functor template
|
call being compiled and executed (which could also be @c void).
|
*/
|
template<bool Pred, typename Then>
|
call_if_statement<Pred, Then> call_if_c(Then f) {
|
return call_if_statement<Pred, Then>(f);
|
}
|
|
/**
|
Select compilation and execution of functor template calls using a nullary
|
boolean meta-function (not needed on C++17 compilers, use <c>if constexpr</c>
|
instead).
|
|
This is equivalent to <c>boost::contract::call_if_c<Pred::value>(f)</c>.
|
Create a call-if object with the specified then-branch functor template:
|
|
@code
|
boost::contract::call_if<Pred1>(
|
then_functor_template1
|
).template else_if<Pred2>( // Optional.
|
then_functor_template2
|
) // Optionally, other `else_if` or
|
... // `else_if_c`.
|
.else_( // Optional for `void` functors,
|
else_functor_template // but required for non `void`.
|
)
|
@endcode
|
|
Optional functor templates for else-if-branches and the else-branch can be
|
specified as needed (the else-branch functor template is required if @c f
|
returns non-void).
|
|
@see @RefSect{extras.assertion_requirements__templates_,
|
Assertion Requirements}
|
|
@param f Then-branch nullary functor template.
|
The functor template call @c f() is compiled and executed if and
|
only if @c Pred::value is @c true.
|
The return type of other functor template calls specified for this
|
call-if statement (else-branch, else-if-branches, etc.) must be the
|
same as (or implicitly convertible to) the return type of
|
then-branch functor template call @c f().
|
|
@tparam Pred Nullary boolean meta-function selecting which functor template
|
call to compile and execute.
|
|
@return A call-if statement so else and else-if statements can be specified if
|
needed.
|
Eventually, this will be the return value of the one functor template
|
call being compiled and executed (which could also be @c void).
|
*/
|
template<class Pred, typename Then>
|
call_if_statement<Pred::value, Then> call_if(Then f) {
|
return call_if_statement<Pred::value, Then>(f);
|
}
|
|
/**
|
Select compilation and execution of a boolean functor template condition using a
|
static boolean predicate (not needed on C++17 compilers, use
|
<c>if constexpr</c> instead).
|
|
Compile and execute the nullary boolean functor template call @c f() if and only
|
if the specified static boolean predicate @p Pred is @c true, otherwise
|
trivially return @p else_ (@c true by default) at run-time.
|
|
A call to <c>boost::contract::condition_if_c<Pred>(f, else_)</c> is logically
|
equivalent to <c>boost::contract::call_if_c<Pred>(f, [] { return else_; })</c>
|
(but its internal implementation is optimized and it does not actually use
|
@c call_if_c).
|
|
@see @RefSect{extras.assertion_requirements__templates_,
|
Assertion Requirements}
|
|
@param f Nullary boolean functor template.
|
The functor template call @c f() is compiled and executed if and
|
only if @c Pred is @c true.
|
|
@tparam Pred Static boolean predicate selecting when the functor template
|
call @c f() should be compiled and executed.
|
@param else_ Boolean value to return when @c Pred is @c false (instead of
|
compiling and executing the functor template call @c f()).
|
|
@return Boolean value returned by @c f() if the static predicate @c Pred is
|
@c true. Otherwise, trivially return @p else_.
|
*/
|
#ifdef BOOST_CONTRACT_DETAIL_DOXYGEN
|
template<bool Pred, typename Then>
|
bool condition_if_c(Then f, bool else_ = true);
|
#else
|
// NOTE: condition_if is a very simple special case of call_if so it can be
|
// trivially implemented using enable_if instead of call_if as done below.
|
|
template<bool Pred, typename Then>
|
typename boost::enable_if_c<Pred, bool>::type
|
condition_if_c(Then f, bool /* else_ */ = true) { return f(); }
|
|
template<bool Pred, typename Then>
|
typename boost::disable_if_c<Pred, bool>::type
|
condition_if_c(Then /* f */, bool else_ = true) { return else_; }
|
#endif
|
|
/**
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Select compilation and execution of a boolean functor template condition using a
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nullary boolean meta-function (not needed on C++17 compilers, use
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<c>if constexpr</c> instead).
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This is equivalent to
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<c>boost::contract::condition_if_c<Pred::value>(f, else_)</c>.
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Compile and execute the nullary boolean functor template call @c f() if and only
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if the specified nullary boolean meta-function @p Pred::value is @c true,
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otherwise trivially return @p else_ (@c true by default) at run-time.
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@see @RefSect{extras.assertion_requirements__templates_,
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Assertion Requirements}
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@param f Nullary boolean functor template.
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The functor template call @c f() is compiled and executed if and
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only if @c Pred::value is @c true.
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@param else_ Boolean value to return when @c Pred::value is @c false (instead
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of compiling and executing the functor template call @c f()).
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@tparam Pred Nullary boolean meta-function selecting when the functor
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template call @c f() should be compiled and executed.
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@return Boolean value returned by @c f() if the static predicate @c Pred::value
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is @c true. Otherwise, trivially return @p else_.
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*/
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template<class Pred, typename Then>
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bool condition_if(Then f, bool else_ = true) {
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return condition_if_c<Pred::value>(f, else_);
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}
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} } // namespace
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#endif // #include guard
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