seqan3::detail::lazy_conditional< decision, on_true_t, on_false_t > Struct Template Reference

Behaves like std::conditional, but instantiates types wrapped in seqan3::lazy. More...

#include <seqan3/utility/type_traits/lazy_conditional.hpp>

Inheritance diagram for seqan3::detail::lazy_conditional< decision, on_true_t, on_false_t >:

Related Symbols
(Note that these are not member symbols.)
template<bool decision, typename on_true_t , typename on_false_t >
using	lazy_conditional_t = instantiate_t< std::conditional_t< decision, on_true_t, on_false_t > >
	Behaves like std::conditional_t, but instantiates types wrapped in seqan3::lazy. Transformation trait shortcut.
Related Symbols inherited from seqan3::detail::instantiate< std::conditional_t< decision, on_true_t, on_false_t > >
using	instantiate_t = typename instantiate< std::conditional_t< decision, on_true_t, on_false_t > >::type
	A transformation trait that instantiates seqan3::lazy types. Transformation trait shortcut.

Detailed Description

template<bool decision, typename on_true_t, typename on_false_t>
struct seqan3::detail::lazy_conditional< decision, on_true_t, on_false_t >

Behaves like std::conditional, but instantiates types wrapped in seqan3::lazy.

Template Parameters

decision	Whether to resolve to the first type or the second.
on_true_t	The return type in case decision is true.
on_false_t	The return type in case decision is false.

Example

// SPDX-FileCopyrightText: 2006-2025 Knut Reinert & Freie Universität Berlin
// SPDX-FileCopyrightText: 2016-2025 Knut Reinert & MPI für molekulare Genetik
// SPDX-License-Identifier: CC0-1.0
 
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-parameter"
#pragma GCC diagnostic ignored "-Wunused-local-typedefs"
 
#include <forward_list> // std::forward_list
#include <ranges>       // std::ranges::input_range
#include <vector>       // std::vector
 
#include <seqan3/core/range/type_traits.hpp>               // seqan3::size_type_t
#include <seqan3/utility/type_traits/lazy_conditional.hpp> // seqan3::lazy_conditional_t
 
template <std::ranges::input_range rng_t>
void foobar(rng_t && range)
{
 
#if 0
    // The following would fail to compile if rng_t is not sized,
    // because std::ranges::range_size_t<rngt_t> needs to be valid
    // (independent of whether the condition evaluates to true)
    using size_type = std::conditional_t<std::ranges::sized_range<rng_t>,
                                         std::ranges::range_size_t<rng_t>,
                                         void>;
#endif
 
    // This delays instantiation of std::ranges::range_size_t<rngt_t> until after the
    // conditional-decision is made:
    using size_type = seqan3::detail::lazy_conditional_t<std::ranges::sized_range<rng_t>,
                                                         seqan3::detail::lazy<std::ranges::range_size_t, rng_t>,
                                                         void>;
 
    // DO SOMETHING with size_type
}
 
int main()
{
    foobar(std::vector<int>{});       // sized
    foobar(std::forward_list<int>{}); // not sized
}
 
#pragma GCC diagnostic pop

complete

Friends And Related Symbol Documentation

lazy_conditional_t

template<bool decision, typename on_true_t , typename on_false_t >

template<bool decision, typename on_true_t , typename on_false_t >

using lazy_conditional_t = instantiate_t<std::conditional_t<decision, on_true_t, on_false_t> >

related

Behaves like std::conditional_t, but instantiates types wrapped in seqan3::lazy. Transformation trait shortcut.

Template Parameters

decision	Whether to resolve to the first type or the second.
on_true_t	The return type in case decision is true.
on_false_t	The return type in case decision is false.

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The documentation for this struct was generated from the following file:

• lazy_conditional.hpp