Panduan C++ Edisi Kelima: Melampaui Pasangan: Pengelompokan Multi-Tipe dengan Tuples

Dalam arsitektur sistem C++ berskala besar, mendefinisikan struktur formal struct untuk setiap pengelompokan data sementara sering kali berlebihan. Objek std::tuple berfungsi sebagai kontainer heterogen, yang memperluas std::pair untuk menyimpan jumlah tak terbatas tipe yang berbeda.

1. Konstruksi & Keterbatasan

Berbeda dengan kontainer standar, konstruktor tuple adalah eksplisit. Anda tidak dapat menggunakan inisialisasi salinan dengan daftar; Anda harus menggunakan inisialisasi langsung atau std::make_tuple.

tuple<int, double> t1{1, 2.5}; // OK
tuple<int, double> t2 = {1, 2.5}; // Kesalahan!

2. Akses & Introspeksi

Anggota diakses melalui get<i>(nama_tuple), di mana i harus merupakan ekspresi konstan yang diketahui pada saat kompilasi. Metadata dapat ditanyakan melalui tuple_size dan tuple_element menggunakan decltype.

3. Logika Relasional

Tuples dibandingkan secara leksikografis. Perbandingan hanya valid jika kedua tuple memiliki jumlah anggota yang sama dan tipe-tipe terkait mendukung operator relasional.

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QUESTION 1

Which of the following tuple initializations will result in a compile-time error?

tuple<int, int> t{1, 2};

auto t = make_tuple(1, 2);

tuple<int, int> t = {1, 2};

tuple<int, int> t(1, 2);

QUESTION 2

What is the requirement for the index i in get(tuple_obj)?

It can be any runtime integer variable.

It must be a constant expression (compile-time constant).

It must be an unsigned integer literal.

The index is ignored; tuples are accessed like queues.

QUESTION 3

Which utility is used to find the number of elements in a tuple type at compile time?

t.size()

sizeof(t)

tuple_size<T>::value

tuple_element<0, T>::size

✅ Correct!

std::tuple_size is a template class that provides the constant value representing the element count.

❌ Incorrect

Tuples do not have a size() member function like vectors; they use compile-time template traits.

QUESTION 4

What happens when you compare two tuples of different sizes (e.g., a 2-tuple vs a 3-tuple)?

The shorter tuple is padded with zeros.

A compile-time error occurs.

The comparison only checks the common prefix.

It returns false by default.

QUESTION 5

How are tuple comparisons (e.g., <) evaluated?

By summing the values of all members.

By comparing the address of the tuple objects.

Lexicographically (element-by-element from index 0).

Only the first member is compared.