std::tie
From cppreference.com
Defined in header
<tuple>
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template< class... Types >
tuple<Types&...> tie( Types&... args ); |
(since C++11) (until C++14) |
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template< class... Types >
constexpr tuple<Types&...> tie( Types&... args ); |
(since C++14) | |
Creates a tuple of lvalue references to its arguments or instances of std::ignore.
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[edit] Parameters
args | - | zero or more lvalue arguments to construct the tuple from |
[edit] Return value
A std::tuple object containing lvalue references.
[edit] Exceptions
noexcept specification:
noexcept
[edit] Notes
std::tie
may be used to unpack a std::pair because std::tuple has a converting assignment from pairs:
bool result; std::tie(std::ignore, result) = set.insert(value);
[edit] Example
std::tie
can be used to introduce lexicographical comparison to a struct or to unpack a tuple:
Run this code
#include <iostream> #include <string> #include <set> #include <tuple> struct S { int n; std::string s; float d; bool operator<(const S& rhs) const { // compares n to rhs.n, // then s to rhs.s, // then d to rhs.d return std::tie(n, s, d) < std::tie(rhs.n, rhs.s, rhs.d); } }; int main() { std::set<S> set_of_s; // S is LessThanComparable S value{42, "Test", 3.14}; std::set<S>::iterator iter; bool inserted; // unpacks the return value of insert into iter and inserted std::tie(iter, inserted) = set_of_s.insert(value); if (inserted) std::cout << "Value was inserted successfully\n"; }
Output:
Value was inserted successfully
creates a tuple object of the type defined by the argument types (function template) |
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creates a tuple of rvalue references (function template) |
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creates a tuple by concatenating any number of tuples (function template) |
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placeholder to skip an element when unpacking a tuple using tie (constant) |