utils::LazyPrvalue< Func > Class Template Reference

Can be used with various emplace functions to allow in-place constructing a non-movable value using a callable. More...

#include <userver/utils/lazy_prvalue.hpp>

Public Member Functions
constexpr	LazyPrvalue (const Func &func)
constexpr	LazyPrvalue (Func &&func)
	LazyPrvalue (LazyPrvalue &&)=delete
LazyPrvalue &	operator= (LazyPrvalue &&)=delete
constexpr	operator std::invoke_result_t< Func && > () &&

Detailed Description

template<typename Func>
class utils::LazyPrvalue< Func >

Can be used with various emplace functions to allow in-place constructing a non-movable value using a callable.

// Suppose that 'NonMovable' comes from an external library.
class NonMovable final {
 public:
  // The only proper way to obtain a 'NonMovable' is through 'Make' factory
  // function.
  static NonMovable Make() { return NonMovable(42); }
 
  NonMovable(NonMovable&&) = delete;
  NonMovable& operator=(NonMovable&&) = delete;
 
  int Get() const { return value_; }
 
 private:
  explicit NonMovable(int value) : value_(value) {}
 
  int value_;
};
 
TEST(LazyPrvalue, Optional) {
  std::optional<NonMovable> opt;
 
  // If 'std::optional', in addition to 'emplace' method, had 'emplace_func',
  // then we could use it to in-place construct 'NonMovable' there. Alas,
  // 'std::optional' has no such method. But we can obtain its functionality
  // using 'utils::LazyPrvalue'.
  opt.emplace(utils::LazyPrvalue([] { return NonMovable::Make(); }));
 
  EXPECT_EQ(opt->Get(), 42);
}

Definition at line 20 of file lazy_prvalue.hpp.

Constructor & Destructor Documentation

LazyPrvalue() [1/2]

template<typename Func >

constexpr utils::LazyPrvalue< Func >::LazyPrvalue ( const Func &  func )

inlineexplicitconstexpr

Definition at line 24 of file lazy_prvalue.hpp.

LazyPrvalue() [2/2]

template<typename Func >

constexpr utils::LazyPrvalue< Func >::LazyPrvalue ( Func &&  func )

inlineexplicitconstexpr

Definition at line 26 of file lazy_prvalue.hpp.

Member Function Documentation

operator std::invoke_result_t< Func && >()

template<typename Func >

constexpr utils::LazyPrvalue< Func >::operator std::invoke_result_t< Func && > ( ) &&

inlineconstexpr

Definition at line 31 of file lazy_prvalue.hpp.

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

• userver/utils/lazy_prvalue.hpp