tmp/tmpfm3a6jz3/{from.md → to.md}
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| 1 |
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## Compile-time integer sequences <a id="intseq">[[intseq]]</a>
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### In general <a id="intseq.general">[[intseq.general]]</a>
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The library provides a class template that can represent an integer
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sequence. When used as an argument to a function template the parameter
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pack defining the sequence can be deduced and used in a pack expansion.
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``` cpp
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template<class F, class Tuple, std::size_t... I>
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decltype(auto) apply_impl(F&& f, Tuple&& t, index_sequence<I...>) {
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return std::forward<F>(f)(std::get<I>(std::forward<Tuple>(t))...);
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}
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template<class F, class Tuple>
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decltype(auto) apply(F&& f, Tuple&& t) {
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using Indices = make_index_sequence<std::tuple_size<std::decay_t<Tuple>>::value>;
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return apply_impl(std::forward<F>(f), std::forward<Tuple>(t), Indices());
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}
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```
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The `index_sequence` alias template is provided for the common case of
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an integer sequence of type `size_t`.
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### Class template `integer_sequence` <a id="intseq.intseq">[[intseq.intseq]]</a>
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``` cpp
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namespace std {
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template<class T, T... I>
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struct integer_sequence {
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typedef T value_type;
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static constexpr size_t size() noexcept { return sizeof...(I); }
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};
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}
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```
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`T` shall be an integer type.
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### Alias template `make_integer_sequence` <a id="intseq.make">[[intseq.make]]</a>
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``` cpp
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template<class T, T N>
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using make_integer_sequence = integer_sequence<T, see below>;
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```
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If `N` is negative the program is ill-formed. The alias template
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`make_integer_sequence` denotes a specialization of `integer_sequence`
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with `N` template non-type arguments. The type
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`make_integer_sequence<T, N>` denotes the type
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`integer_sequence<T, 0, 1, ..., N-1>`. `make_integer_sequence<int, 0>`
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denotes the type `integer_sequence<int>`
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