Provides metaprogramming utilities for working on template parameter packs.
More...
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template<typename unary_predicate_t , typename... pack_t>
requires (std::predicate<unary_predicate_t, pack_t> && ...) |
constexpr bool | seqan3::detail::all_of (unary_predicate_t &&fn, pack_t &&... args) |
| Tests whether a given predicate evaluates to true for each element in the function parameter pack.
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template<ptrdiff_t idx, typename head_t , typename... tail_t> |
auto | seqan3::pack_traits::detail::at () |
| Implementation for seqan3::pack_traits::at.
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template<typename head_t , typename... tail_t> |
type_list< tail_t... > | seqan3::pack_traits::detail::drop_front () |
| Implementation for seqan3::pack_traits::drop_front.
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template<typename query_t , typename... pack_t> |
constexpr ptrdiff_t | seqan3::pack_traits::detail::find () |
| Implementation for seqan3::pack_traits::find.
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template<template< typename > typename pred_t, typename... pack_t> |
constexpr ptrdiff_t | seqan3::pack_traits::detail::find_if () |
| Implementation for seqan3::pack_traits::find_if.
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template<typename unary_function_t , typename... pack_t>
requires (std::invocable<unary_function_t, pack_t> && ...) |
constexpr void | seqan3::detail::for_each (unary_function_t &&fn, pack_t &&... args) |
| Applies a function to each element of the given function parameter pack.
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template<typename head_t , typename... tail_t> |
std::type_identity< head_t > | seqan3::pack_traits::detail::front () |
| Implementation for seqan3::pack_traits::front.
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template<typename replace_t , ptrdiff_t idx, typename... pack_t, size_t... i> |
auto | seqan3::pack_traits::detail::replace_at (std::index_sequence< i... >) -> type_list< std::conditional_t< i==idx, replace_t, pack_t >... > |
| Implementation for seqan3::pack_traits::replace_at.
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template<ptrdiff_t idx, typename head_t , typename... pack2_t, typename... pack1_t> |
auto | seqan3::pack_traits::detail::split_after (type_list< pack1_t... >) |
| Implementation for seqan3::pack_traits::split_after.
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template<ptrdiff_t idx, typename... pack_t> |
using | seqan3::pack_traits::at = typename decltype(detail::at< idx, pack_t... >())::type |
| Return the type at given index from the type pack.
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template<typename... pack_t> |
using | seqan3::pack_traits::front = typename decltype(detail::front< pack_t... >())::type |
| Return the first type from the type pack.
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template<typename... pack_t> |
using | seqan3::pack_traits::back = typename decltype((std::type_identity< pack_t >{},...))::type |
| Return the last type from the type pack.
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template<typename... pack_t> |
using | seqan3::pack_traits::drop_front = typename decltype(detail::drop_front< pack_t... >())::type |
| Return a seqan3::type_list of all the types in the type pack, except the first.
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template<template< typename > typename trait_t, typename... pack_t> |
using | seqan3::pack_traits::transform = seqan3::type_list< trait_t< pack_t >... > |
| Apply a transformation trait to every type in the pack and return a seqan3::type_list of the results.
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template<ptrdiff_t i, typename... pack_t> |
using | seqan3::pack_traits::take = typename decltype(detail::split_after< i, pack_t... >(type_list<>{}))::first_type |
| Return a seqan3::type_list of the first n types in the type pack.
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template<ptrdiff_t i, typename... pack_t> |
using | seqan3::pack_traits::drop = typename decltype(detail::split_after< i, pack_t... >(type_list<>{}))::second_type |
| Return a seqan3::type_list of the types in the type pack, except the first n .
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template<ptrdiff_t i, typename... pack_t> |
using | seqan3::pack_traits::take_last = drop< size< pack_t... > - i, pack_t... > |
| Return a seqan3::type_list of the last n types in the type pack.
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template<ptrdiff_t i, typename... pack_t> |
using | seqan3::pack_traits::drop_last = take< size< pack_t... > - i, pack_t... > |
| Return a seqan3::type_list of the types the type pack, except the last n .
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template<ptrdiff_t i, typename... pack_t> |
using | seqan3::pack_traits::split_after = decltype(detail::split_after< i, pack_t... >(type_list<>{})) |
| Split a type pack into two parts returned as a pair of seqan3::type_list.
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template<typename replace_t , std::ptrdiff_t i, typename... pack_t> |
using | seqan3::pack_traits::replace_at = decltype(detail::replace_at< replace_t, i, pack_t... >(std::make_index_sequence< size< pack_t... > >{})) |
| Replace the type at the given index with the given type.
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template<typename... pack_t> |
constexpr size_t | seqan3::pack_traits::size = sizeof...(pack_t) |
| The size of a type pack.
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template<typename query_t , typename... pack_t> |
constexpr ptrdiff_t | seqan3::pack_traits::count = (std::is_same_v<query_t, pack_t> + ... + 0) |
| Count the occurrences of a type in a pack.
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template<typename query_t , typename... pack_t> |
constexpr ptrdiff_t | seqan3::pack_traits::find = seqan3::pack_traits::detail::find<query_t, pack_t...>() |
| Get the index of the first occurrence of a type in a pack.
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template<template< typename > typename pred_t, typename... pack_t> |
constexpr ptrdiff_t | seqan3::pack_traits::find_if = seqan3::pack_traits::detail::find_if<pred_t, pack_t...>() |
| Get the index of the first type in a pack that satisfies the given predicate.
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template<typename query_t , typename... pack_t> |
constexpr bool | seqan3::pack_traits::contains = (find<query_t, pack_t...> != -1) |
| Whether a type occurs in a pack or not.
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Provides metaprogramming utilities for working on template parameter packs.
- See also
- Utility
This module contains auxiliary functions, algorithms and traits on template parameter packs. All traits on a template parameter pack are defined in the header <seqan3/utility/type_pack/traits.hpp>
.
◆ at
template<ptrdiff_t idx, typename... pack_t>
Return the type at given index from the type pack.
- Template Parameters
-
idx | The index; must be smaller than the size of the pack. |
pack_t | The type pack. |
Negative indexes are supported (e.g. at<-1, int, double, bool &>
is bool &
).
(Compile-time) Complexity
- Number of template instantiations: O(n)
- Other operations: O(n)
int main()
{
static_assert(std::same_as<float, seqan3::pack_traits::at<1, int, float, bool, double>>);
}
typename decltype(detail::at< idx, pack_t... >())::type at
Return the type at given index from the type pack.
Definition type_pack/traits.hpp:245
Provides various traits for template packs.
◆ back
template<typename... pack_t>
Return the last type from the type pack.
- Template Parameters
-
(Compile-time) Complexity
- Number of template instantiations: O(n) (possibly O(1))
- Other operations: O(1)
Notably faster than seqan3::pack_traits::at<size<pack...> - 1, pack...>
(no recursive template instantiations).
int main()
{
static_assert(std::same_as<float, seqan3::pack_traits::back<int, float, bool, int, float>>);
}
◆ drop
template<ptrdiff_t i, typename... pack_t>
Return a seqan3::type_list of the types in the type pack, except the first n
.
- Template Parameters
-
i | The amount to drop; must be >= 0 and <= the size of the type pack. |
pack_t | The type pack. |
(Compile-time) Complexity
- Number of template instantiations: O(n)
- Other operations: O(n)
int main()
{
}
typename decltype(detail::split_after< i, pack_t... >(type_list<>{}))::second_type drop
Return a seqan3::type_list of the types in the type pack, except the first n.
Definition type_pack/traits.hpp:367
◆ drop_front
template<typename... pack_t>
Return a seqan3::type_list of all the types in the type pack, except the first.
- Template Parameters
-
(Compile-time) Complexity
- Number of template instantiations: O(1)
- Other operations: O(1)
int main()
{
static_assert(
}
typename decltype(detail::drop_front< pack_t... >())::type drop_front
Return a seqan3::type_list of all the types in the type pack, except the first.
Definition type_pack/traits.hpp:305
◆ drop_last
template<ptrdiff_t i, typename... pack_t>
Return a seqan3::type_list of the types the type pack, except the last n
.
- Template Parameters
-
i | The amount to drop; must be >= 0 and <= the size of the type pack. |
pack_t | The type pack. |
(Compile-time) Complexity
- Number of template instantiations: O(n)
- Other operations: O(n)
int main()
{
}
drop< size< pack_t... > - i, pack_t... > take_last
Return a seqan3::type_list of the last n types in the type pack.
Definition type_pack/traits.hpp:385
◆ front
template<typename... pack_t>
Return the first type from the type pack.
- Template Parameters
-
(Compile-time) Complexity
- Number of template instantiations: O(1)
- Other operations: O(1)
int main()
{
static_assert(std::same_as<int, seqan3::pack_traits::front<int, float, bool, int, float>>);
}
◆ replace_at
Replace the type at the given index with the given type.
- Template Parameters
-
replace_t | The type to replace the old type with. |
i | The index of the type to be replaced. |
pack_t | The (input) type pack. |
(Compile-time) Complexity
- Number of template instantiations: O(n)
- Other operations: O(n)
◆ split_after
template<ptrdiff_t i, typename... pack_t>
Split a type pack into two parts returned as a pair of seqan3::type_list.
- Template Parameters
-
i | The number of elements after which to split; must be >= 0 and <= the size of the type pack. |
pack_t | The type pack. |
(Compile-time) Complexity
- Number of template instantiations: O(n)
- Other operations: O(n)
◆ take
template<ptrdiff_t i, typename... pack_t>
Return a seqan3::type_list of the first n
types in the type pack.
- Template Parameters
-
i | The target size; must be >= 0 and <= the size of the type pack. |
pack_t | The type pack. |
(Compile-time) Complexity
- Number of template instantiations: O(n)
- Other operations: O(n)
int main()
{
}
typename decltype(detail::split_after< i, pack_t... >(type_list<>{}))::first_type take
Return a seqan3::type_list of the first n types in the type pack.
Definition type_pack/traits.hpp:349
◆ take_last
template<ptrdiff_t i, typename... pack_t>
Return a seqan3::type_list of the last n
types in the type pack.
- Template Parameters
-
i | The target size; must be >= 0 and <= the size of the type pack. |
pack_t | The type pack. |
(Compile-time) Complexity
- Number of template instantiations: O(n)
- Other operations: O(n)
◆ transform
template<template< typename > typename trait_t, typename... pack_t>
Apply a transformation trait to every type in the pack and return a seqan3::type_list of the results.
- Template Parameters
-
trait_t | The transformation trait, can be an alias template, e.g. a transformation trait shortcut. |
pack_t | The type pack. |
The transformation trait given as first argument can be an alias template, e.g. std::type_identity_t, not std::type_identity. The alias must take exactly one argument and be defined for all types in the pack.
(Compile-time) Complexity
- Number of template instantiations: O(n)
- Other operations: O(1)
int main()
{
static_assert(std::same_as<
seqan3::pack_traits::
}
Provides various transformation traits used by the range module.
Type that contains multiple types.
Definition type_list.hpp:26
◆ all_of()
template<typename unary_predicate_t , typename... pack_t>
requires (std::predicate<unary_predicate_t, pack_t> && ...)
constexpr bool seqan3::detail::all_of |
( |
unary_predicate_t && |
fn, |
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pack_t &&... |
args |
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) |
| |
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constexpr |
Tests whether a given predicate evaluates to true
for each element in the function parameter pack.
- Template Parameters
-
unary_predicate_t | The function type, like function pointers, functors and lambdas; must model std::predicate expanded on each argument type. |
pack_t | The parameter pack of the arguments (each argument type can be different). |
- Parameters
-
[in] | fn | The predicate to evaluate for every argument. |
[in] | args | The parameter pack. |
- Returns
true
if the predicate returns true
for each type in the type list, false
otherwise.
This function behaves like std::all_of but on parameter packs. The invocation(s) will be done without any loop.
Example
auto fn = [](auto value)
{
using value_t = decltype(value);
if constexpr (std::is_same_v<value_t, bool>)
return value == false;
else if constexpr (std::is_same_v<value_t, int>)
return value == 3;
else if constexpr (std::is_same_v<value_t, double>)
return value - 1.2 < 0.00001;
else
return false;
};
constexpr bool all_of(unary_predicate_t &&fn)
Tests whether a given predicate evaluates to true for each type in a seqan3::type_list.
Definition type_list_algorithm.hpp:107
Provides algorithms for meta programming, parameter packs and seqan3::type_list.
Complexity
Linear in the number of elements in the pack.
- Attention
- Opposed to the std::all_of the argument order is changed, such that the first argument is the unary predicate to invoke on each argument followed by the arguments. This is due to a constraint in the c++ language regarding parameter packs.
- See also
- https://en.cppreference.com/w/cpp/language/parameter_pack
◆ at()
template<ptrdiff_t idx, typename head_t , typename... tail_t>
auto seqan3::pack_traits::detail::at |
( |
| ) |
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Implementation for seqan3::pack_traits::at.
- Template Parameters
-
idx | The index. |
head_t | Currently viewed pack_t element. |
tail_t | Rest of the type pack. |
◆ drop_front()
template<typename head_t , typename... tail_t>
type_list< tail_t... > seqan3::pack_traits::detail::drop_front |
( |
| ) |
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◆ find()
template<typename query_t , typename... pack_t>
constexpr ptrdiff_t seqan3::pack_traits::detail::find |
( |
| ) |
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constexpr |
Implementation for seqan3::pack_traits::find.
- Template Parameters
-
query_t | The type you are searching for. |
pack_t | The type pack. |
- Returns
- The position of the first occurrence of
query_t
in pack_t
or -1
if it is not contained.
◆ find_if()
template<template< typename > typename pred_t, typename... pack_t>
constexpr ptrdiff_t seqan3::pack_traits::detail::find_if |
( |
| ) |
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constexpr |
Implementation for seqan3::pack_traits::find_if.
- Template Parameters
-
pred_t | The predicate that is being evaluated. |
pack_t | The type pack. |
- Returns
- The position of the first type
t
in pack_t
for whom pred_t<t>::value
is true.
◆ for_each()
template<typename unary_function_t , typename... pack_t>
requires (std::invocable<unary_function_t, pack_t> && ...)
constexpr void seqan3::detail::for_each |
( |
unary_function_t && |
fn, |
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|
pack_t &&... |
args |
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) |
| |
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constexpr |
Applies a function to each element of the given function parameter pack.
- Template Parameters
-
unary_function_t | The function type, like function pointers, functors and lambdas. |
pack_t | The parameter pack of the arguments (each argument type can be different). |
- Parameters
-
[in] | fn | The function to call on every argument. |
[in] | args | The parameter pack. |
This function behaves like std::for_each but on parameter packs. The invocation(s) will be done without any loop.
Example
int main()
{
auto fn = [](auto && a)
{
};
fn(0);
fn(", ");
fn(1.0);
fn(", ");
fn('\n');
return 0;
}
Provides seqan3::debug_stream and related types.
debug_stream_type debug_stream
A global instance of seqan3::debug_stream_type.
Definition debug_stream.hpp:37
constexpr void for_each(unary_function_t &&fn)
Applies a function element wise to all types of a type list.
Definition type_list_algorithm.hpp:157
Complexity
Linear in the number of elements in the pack.
- Attention
- Opposed to the std::for_each the argument order is changed, such that the first argument is the unary function to invoke on each argument followed by the arguments. This is due to a constraint in the c++ language regarding parameter packs.
- See also
- https://en.cppreference.com/w/cpp/language/parameter_pack
◆ front()
template<typename head_t , typename... tail_t>
Implementation for seqan3::pack_traits::front.
- Template Parameters
-
head_t | Currently viewed pack_t element. |
tail_t | Rest of the type pack. |
◆ replace_at()
template<typename replace_t , ptrdiff_t idx, typename... pack_t, size_t... i>
Implementation for seqan3::pack_traits::replace_at.
- Template Parameters
-
replace_t | The type replacing the old one. |
idx | The index of the type to replace. |
pack_t | The type pack to be modified. |
i | The indicies of the index sequence associated with the type pack. |
◆ split_after()
template<ptrdiff_t idx, typename head_t , typename... pack2_t, typename... pack1_t>
auto seqan3::pack_traits::detail::split_after |
( |
type_list< pack1_t... > |
| ) |
|
Implementation for seqan3::pack_traits::split_after.
- Template Parameters
-
idx | The index to split the type pack at. |
pack1_t | The type pack before the split index. |
head_t | The next type that is moved before split index. |
pack2_t | The type pack after the split index. |
◆ contains
template<typename query_t , typename... pack_t>
constexpr bool seqan3::pack_traits::contains = (find<query_t, pack_t...> != -1) |
|
inlineconstexpr |
Whether a type occurs in a pack or not.
- Template Parameters
-
query_t | The type you are searching for. |
pack_t | The type pack. |
- Returns
true
or false
.
(Compile-time) Complexity
- Number of template instantiations: O(1)
- Other operations: O(n), possibly ==
i
, where i
is the index of the first occurrence
int main()
{
static_assert(seqan3::pack_traits::find<double, int, float, bool> == -1);
static_assert(seqan3::pack_traits::find<bool, int, float, bool> == 2);
}
◆ count
template<typename query_t , typename... pack_t>
constexpr ptrdiff_t seqan3::pack_traits::count = (std::is_same_v<query_t, pack_t> + ... + 0) |
|
inlineconstexpr |
Count the occurrences of a type in a pack.
- Template Parameters
-
query_t | The type you are searching for. |
pack_t | The type pack. |
- Returns
- The number of occurrences of the
query_t
in pack_t
.
(Compile-time) Complexity
- Number of template instantiations: O(1)
- Other operations: O(n)
int main()
{
static_assert(seqan3::pack_traits::count<int, int, float, bool, int> == 2);
}
◆ find
template<typename query_t , typename... pack_t>
constexpr ptrdiff_t seqan3::pack_traits::find = seqan3::pack_traits::detail::find<query_t, pack_t...>() |
|
inlineconstexpr |
Get the index of the first occurrence of a type in a pack.
- Template Parameters
-
query_t | The type you are searching for. |
pack_t | The type pack. |
- Returns
- The position of the first occurrence of
query_t
in pack_t
or -1
if it is not contained.
(Compile-time) Complexity
- Number of template instantiations: O(1)
- Other operations: O(n), possibly ==
i
, where i
is the return value
int main()
{
static_assert(seqan3::pack_traits::find<double, int, float, bool> == -1);
static_assert(seqan3::pack_traits::find<bool, int, float, bool> == 2);
}
◆ find_if
template<template< typename > typename pred_t, typename... pack_t>
constexpr ptrdiff_t seqan3::pack_traits::find_if = seqan3::pack_traits::detail::find_if<pred_t, pack_t...>() |
|
inlineconstexpr |
Get the index of the first type in a pack that satisfies the given predicate.
- Template Parameters
-
pred_t | The predicate that is being evaluated (a class template). |
pack_t | The type pack. |
- Returns
- The index or
-1
if no types match.
Note that the predicate must be given as a type template (variable templates cannot be passed as template arguments unfortunately). This means e.g. find_if<std::is_integral, float, double, int, float>
(not std::is_integral_v
!).
(Compile-time) Complexity
- Number of template instantiations: O(n), possibly ==
i
, where i
is the return value
Other operations: O(n), possibly == i
, where i
is the return value
Only the predicate is instantiated.
int main()
{
static_assert(seqan3::pack_traits::find_if<std::is_pointer, int, float, double> == -1);
static_assert(seqan3::pack_traits::find_if<std::is_integral, int, float, double> == 0);
}
◆ size
template<typename... pack_t>
constexpr size_t seqan3::pack_traits::size = sizeof...(pack_t) |
|
inlineconstexpr |
The size of a type pack.
- Template Parameters
-
- Returns
sizeof...(pack_t)
(Compile-time) Complexity
- Number of template instantiations: O(1)
- Other operations: O(1)
int main()
{
static_assert(seqan3::pack_traits::size<int, float, bool, int> == 4);
}