// ==========================================================================
//                 SeqAn - The Library for Sequence Analysis
// ==========================================================================
// Copyright (c) 2006-2016, Knut Reinert, FU Berlin
// All rights reserved.
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// modification, are permitted provided that the following conditions are met:
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// ==========================================================================
// Author: Manuel Holtgrewe <manuel.holtgrewe@fu-berlin.de>
// ==========================================================================
// "enable if" functionality.
// ==========================================================================

// SEQAN_NO_GENERATED_FORWARDS

// TODO(holtgrew): Rename *2 Metafunctions to *C metafunctions.
// TODO(holtgrew): Document properly.

#ifndef SEQAN_INCLUDE_SEQAN_BASIC_METAPROGRAMMING_ENABLE_IF_H_
#define SEQAN_INCLUDE_SEQAN_BASIC_METAPROGRAMMING_ENABLE_IF_H_

namespace seqan {

// ============================================================================
// Forwards
// ============================================================================

// ============================================================================
// Tags, Classes, Enums
// ============================================================================

// ============================================================================
// Metafunctions
// ============================================================================

/*!
 * @defgroup EnableIfFunctionality Enable-If Functionality
 * @brief The metafunctions and macros for enabling/disabling of functions.
 *
 * The <tt>EnableIf</tt> metafunctions also support the shortcut to <tt>::Type</tt> members as described for the @link
 * LogicMetaprogramming logical metaprogramming metafunctions @endlink.
 *
 * <b>Enable-if is an advanced technique and mostly interesting if you want to extend the SeqAn library with generic
 * algorithms.  The average developer does not have to know about this technique.</b>.
 *
 * @see LogicalValuesTags
 * @see LogicMetaprogramming
 */

// ----------------------------------------------------------------------------
// Metafunction EnableIf
// ----------------------------------------------------------------------------

/*!
 * @mfn EnableIfFunctionality#EnableIf
 * @headerfile <seqan/basic.h>
 * @brief Metafunction to use for conditionally enabling code.
 *
 * @signature EnableIf<TBool, T = void>::Type
 *
 * @tparam TBool The Tag <tt>True</tt> or <tt>False</tt> to use for enabling/disabling.
 * @tparam T     Dummy, do not set.
 *
 * @return Type Set to <tt>T</tt>.  Only defined if <tt>TBool</tt> is <tt>True</tt>.  This triggers the SFINAE behaviour
 *              in C++ which can be used to enable/disable functions.
 *
 * Do not use directly but use through the enable if/disable if macros.
 *
 * @see EnableIfFunctionality#SEQAN_FUNC_ENABLE_IF
 * @see EnableIfFunctionality#SEQAN_FUNC_DISABLE_IF
 * @see EnableIfFunctionality#SEQAN_CTOR_ENABLE_IF
 * @see EnableIfFunctionality#SEQAN_CTOR_DISABLE_IF
 */

template <typename TBool, typename T = void>
struct EnableIf : EnableIf<typename TBool::Type, T> {};

template <typename T>
struct EnableIf<False, T> {};

template <typename T>
struct EnableIf<True, T>
{
    typedef T Type;
};

//template <typename T>
//struct EnableIf<False, T> {};

// ----------------------------------------------------------------------------
// Metafunction DisableIf
// ----------------------------------------------------------------------------

/*!
 * @mfn EnableIfFunctionality#DisableIf
 * @headerfile <seqan/basic.h>
 * @brief Metafunction to use for conditionally disabling code.
 *
 * @signature DisableIf<TBool, T = void>::Type
 *
 * @tparam TBool The Tag <tt>True</tt> or <tt>False</tt> to use for enabling/disabling.
 * @tparam T     Dummy, do not set.
 *
 * @return Type Set to <tt>T</tt>.  Only defined if <tt>TBool</tt> is <tt>False</tt>.  This triggers the SFINAE behaviour
 *              in C++ which can be used to enable/disable functions.
 *
 * Do not use directly but use through the enable if/disable if macros.
 *
 * @see EnableIfFunctionality#SEQAN_FUNC_ENABLE_IF
 * @see EnableIfFunctionality#SEQAN_FUNC_DISABLE_IF
 * @see EnableIfFunctionality#SEQAN_CTOR_ENABLE_IF
 * @see EnableIfFunctionality#SEQAN_CTOR_DISABLE_IF
 */

template <typename TBool, typename T = void>
struct DisableIf : DisableIf<typename TBool::Type, T> {};

template <typename T>
struct DisableIf<True, T> {};

template <typename T>
struct DisableIf<False, T>
{
    typedef T Type;
};

// ----------------------------------------------------------------------------
// Metafunction EnableIf2
// ----------------------------------------------------------------------------

/*!
 * @mfn EnableIfFunctionality#EnableIf2
 * @headerfile <seqan/basic.h>
 * @deprecated Will be renamed to EnableIfC.
 * @brief Metafunction to use for conditionally enabling code, bool version.
 *
 * @signature EnableIf2<BOOL, T = void>::Type
 *
 * @tparam BOOL The <tt>bool</tt> constant to evaluate for enabling/disabling.
 * @tparam T    Dummy, do not set.
 *
 * @return Type Set to <tt>T</tt>.  Only defined if <tt>BOOL</tt> is <tt>true</tt>.  This triggers the SFINAE behaviour
 *              in C++ which can be used to enable/disable functions.
 *
 * Do not use directly but use through the enable if/disable if macros.
 *
 * @see EnableIfFunctionality#SEQAN_FUNC_ENABLE_IF
 * @see EnableIfFunctionality#SEQAN_FUNC_DISABLE_IF
 * @see EnableIfFunctionality#SEQAN_CTOR_ENABLE_IF
 * @see EnableIfFunctionality#SEQAN_CTOR_DISABLE_IF
 */

//
// Example for enable-if function:
//
//    template <typename TContainer>
//    typename EnableIf<
//        IsContainer<TContainer>,                  // 1st arg: enable-if condition
//        typename Size<TContainer>::Type >::Type   // 2nd arg: return type
//    length(TContainer & cont)
//    {
//        SEQAN_CONCEPT_ASSERT((ContainerConcept<TContainer>));
//        return end(cont) - begin(cont);
//    }

template <bool b, typename T>
struct EnableIf2;

template <bool b, typename T = void>
struct EnableIf2
{
    typedef T Type;
};

template <typename T>
struct EnableIf2<false, T> {};

// ----------------------------------------------------------------------------
// Metafunction DisableIf2
// ----------------------------------------------------------------------------

/*!
 * @mfn EnableIfFunctionality#DisableIf2
 * @headerfile <seqan/basic.h>
 * @deprecated Will be renamed to DisableIfC.
 * @brief Metafunction to use for conditionally disabling code, bool version.
 *
 * @signature DisableIf2<BOOL, T = void>::Type
 *
 * @tparam BOOL The <tt>bool</tt> constant to evaluate for enabling/disabling.
 * @tparam T    Dummy, do not set.
 *
 * @return Type Set to <tt>T</tt>.  Only defined if <tt>BOOL</tt> is <tt>false</tt>.  This triggers the SFINAE behaviour
 *              in C++ which can be used to enable/disable functions.
 *
 * Do not use directly but use through the enable if/disable if macros.
 *
 * @see EnableIfFunctionality#SEQAN_FUNC_ENABLE_IF
 * @see EnableIfFunctionality#SEQAN_FUNC_DISABLE_IF
 * @see EnableIfFunctionality#SEQAN_CTOR_ENABLE_IF
 * @see EnableIfFunctionality#SEQAN_CTOR_DISABLE_IF
 */

template <bool b, typename T>
struct DisableIf2;

template <bool b, typename T = void>
struct DisableIf2
{
    typedef T Type;
};

template <typename T>
struct DisableIf2<true, T> {};

}  // namespace seqan

// ============================================================================
// Macros
// ============================================================================

/*!
 * @macro EnableIfFunctionality#SEQAN_CTOR_ENABLE_IF
 * @headerfile <seqan/basic.h>
 * @brief Bind the visibility of a constructor to an expression.
 *
 * @signature SEQAN_CTOR_ENABLE_IF(TCondition);
 *
 * @param TCondition Boolean type, one of <tt>True</tt> and <tt>False</tt> or a metafunction returning such a tag
 *                   type.  If <tt>True</tt> then the constructor is visible, otherwise, it is not.
 *
 * This macro allows one to bind the visibility of a construtor to a boolean expression by using the <a
 * href="http://en.wikipedia.org/wiki/Substitution_failure_is_not_an_error">SFINAE</a> principle for an optional argument with default value.  The macro call must be used as the last dummy-argument of a constructor.
 *
 * To avoid an unused argument warning, call <tt>ignoreUnusedVariableWarning(dummy)</tt> in the constructor's body.
 *
 * <b>Important:</b> The constructor to enable must be a function template and <tt>TCondition</tt> must include at
 * least one template parameter of the function template.
 *
 * @section Example
 *
 * The following shows an example on how to properly use <tt>SEQAN_CTOR_ENABLE_IF</tt> as the last argument to the
 * constructor and suppressing the unused variable warning for the dummy parameter.
 *
 * @snippet demos/dox/basic/enable_if.cpp enable if example constructor
 */

#define SEQAN_CTOR_ENABLE_IF(...) typename seqan::EnableIf<__VA_ARGS__>::Type * dummy = 0

/*!
 * @macro EnableIfFunctionality#SEQAN_CTOR_DISABLE_IF
 * @headerfile <seqan/basic.h>
 * @brief Bind the visibility of a constructor to an expression.
 *
 * @signature SEQAN_CTOR_DISABLE_IF(TCondition);
 *
 * @param TCondition Boolean type, one of <tt>True</tt> and <tt>False</tt> or a metafunction returning such a tag
 *                   type.  If <tt>False</tt> then the constructor is visible, otherwise, it is not.
 *
 * This macro allows one to bind the visibility of a construtor to a boolean expression by using the <a
 * href="http://en.wikipedia.org/wiki/Substitution_failure_is_not_an_error">SFINAE</a> principle for an optional argument with default value.  The macro call must be used as the last dummy-argument of a constructor.
 *
 * To avoid an unused argument warning, call <tt>ignoreUnusedVariableWarning(dummy)</tt> in the constructor's body.
 *
 * <b>Important:</b> The constructor to disable must be a function template and <tt>TCondition</tt> must include at
 * least one template parameter of the function template.
 *
 * @section Example
 *
 * The following shows an example on how to properly use <tt>SEQAN_CTOR_DISABLE_IF</tt> as the last argument to the
 * constructor and suppressing the unused variable warning for the dummy parameter.
 *
 * @snippet demos/dox/basic/enable_if.cpp disable if example constructor
 */

#define SEQAN_CTOR_DISABLE_IF(...) typename seqan::DisableIf<__VA_ARGS__>::Type * dummy = 0

/*!
 * @macro EnableIfFunctionality#SEQAN_FUNC_ENABLE_IF
 * @headerfile <seqan/basic.h>
 * @brief Bind the visibility of a function to an expression.
 *
 * @signature SEQAN_FUNC_ENABLE_IF(TCondition, TResult);
 *
 * @param TCondition Boolean type, one of <tt>True</tt> and <tt>False</tt> or a metafunction returning such a tag
 *                   type.  If <tt>True</tt> then the function is visible, otherwise, it is not.
 * @param TResult    The type that the function should have as the return type in case it is enabled.
 *
 * This macro allows one to bind the visibility of a construtor to a boolean expression by using the <a
 * href="http://en.wikipedia.org/wiki/Substitution_failure_is_not_an_error">SFINAE</a> principle for an optional argument with default value.  The macro call must occur as the return type definition of the function.
 *
 * To avoid an unused argument warning, call <tt>ignoreUnusedVariableWarning(dummy)</tt> in the constructor's body.
 *
 * <b>Important:</b> The function to enable must be a function template and <tt>TCondition</tt> must include at
 * least one template parameter of the function template.
 *
 * @section Example
 *
 * The following shows an example on how to properly use <tt>SEQAN_FUNC_ENABLE_IF</tt> as the last argument to the
 * constructor and suppressing the unused variable warning for the dummy parameter.
 *
 * @snippet demos/dox/basic/enable_if.cpp enable if example function
 */

#define SEQAN_FUNC_ENABLE_IF(...) typename seqan::EnableIf<__VA_ARGS__>::Type

/*!
 * @macro EnableIfFunctionality#SEQAN_FUNC_DISABLE_IF
 * @headerfile <seqan/basic.h>
 * @brief Bind the visibility of a function to an expression.
 *
 * @signature SEQAN_FUNC_DISABLE_IF(TCondition, TResult);
 *
 * @param TCondition Boolean type, one of <tt>True</tt> and <tt>False</tt> or a metafunction returning such a tag
 *                   type.  If <tt>False</tt> then the function is visible, otherwise, it is not.
 * @param TResult    The type that the function should have as the return type in case it is enabled.
 *
 * This macro allows one to bind the visibility of a construtor to a boolean expression by using the <a
 * href="http://en.wikipedia.org/wiki/Substitution_failure_is_not_an_error">SFINAE</a> principle for an optional argument with default value.  The macro call must occur as the return type definition of the function.
 *
 * To avoid an unused argument warning, call <tt>ignoreUnusedVariableWarning(dummy)</tt> in the constructor's body.
 *
 * <b>Important:</b> The function to disable must be a function template and <tt>TCondition</tt> must include at least
 * one template parameter of the function template.
 *
 * @section Example
 *
 * The following shows an example on how to properly use <tt>SEQAN_FUNC_DISABLE_IF</tt> as the last argument to the
 * constructor and suppressing the unused variable warning for the dummy parameter.
 *
 * @snippet demos/dox/basic/enable_if.cpp disable if example function
 */

#define SEQAN_FUNC_DISABLE_IF(...) typename seqan::DisableIf<__VA_ARGS__>::Type

// ============================================================================
// Functions
// ============================================================================

#endif  // #ifndef SEQAN_INCLUDE_SEQAN_BASIC_METAPROGRAMMING_ENABLE_IF_H_
