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Questions tagged [boost-optional]

A Boost C++ library that provides a container that can represent uninitialized objects of arbitrary type, notably allowing easier definition of functions that might not have a value to return

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Comparison (<), output (<<) and assignment (=) for boost::optional

I have a few questions about how boost::optional works. Let's first do this: boost::optional i; Is i < 3 always equivalent to *i < 3 (and similar for other relational operators)? Is it correct that the conditions i < 3 and *i < 3 are…
roger.james
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boost::optional deprecated get_value_or

I suspect boost::optional's get_value_or was deprecated because it is unsafe if an rvalue is passed as the default parameter. However, it is occasionally useful to be able to reference the optional value or a default alternative. Is the following…
Rai
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Can optional be implemented as 8-byte object?

Is it possible to implement std::optional such that sizeof(std::optional) == 8 by somehow using that you can store characters in a NAN, see http://en.cppreference.com/w/cpp/numeric/math/nan? Are there implementations that do that? Can it be…
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How to disengage std::experimental::optional?

With Boost I can create an optional in-place with: boost::optional work = boost::in_place(boost::ref(io_service)); And disengage it with: work = boost::none; With C++14 / experimental support, I can instead…
Riot
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What is boost::optional efficiency?

I have the following: class Obj; typedef std::map StrMap; std::map > complexMap; The thing is that for some entries in complexMap the StrMap will be empty and I won't use it at all, so for…
Subway
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Mixing boost's multi_array and optional with C++11 unique_ptr not working

I've put together a bleeding edge setup with G++ 4.7 (though for the moment I'm still using the boost 1.48 that came with sudo apt-get boost-all-dev on Debian Wheezy). My code is set up where the logical data structure to use would be…
HostileFork says dont trust SE
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Why is boost::optional not convertable to bool for the purposes of std::is_convertible

I have auto result = std::is_convertible < boost::optional , bool >::value; static_assert( result , "task should return bool" ); and it fails to compile. The definition of std::is_convertible is template< class From, class To >…
bradgonesurfing
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I've written C++ code to treat boost::optional as a range but it doesn't compile

I wish to treat boost::optional as a container that can have zero or one elements in it. Logically I should be able to create an iterator to the container and use boost::for_each on it as well. My attempt is below but it fails to compile. I have…
bradgonesurfing
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boost optional recognizes inheritance?

class Base {}; class Derived : public Base {}; void func(boost::optional&) {} int main () { boost::optional x; func(x); } will func accept both optionals: base and derived?
mkmostafa
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Boost Optional implicit conversion to bool?

I'm reading some code and I came across something I do not understand. Its about testing if a Boost::optional value is initialised or not. It uses the gtest framework which provides the ASSERT_TRUE() macro. #include "gtest\gtest.h" void test() { …
Ventu
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boost::optional return from function

I am reviewing some production code where a function says it will return a boost::optional, but it just returns a double: e.g. boost::optional Foo(){ double a = 1.0; double b = 2.0; return a + b; } Is this acceptable style/are…
frickskit
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boost::optional reference with boost::variant type

I'm currently writing some code for a game and part of that involves creating a history of the actions that have taken place so far in the game. This history is stored in a vector of state_pair_t's pairs of actions (action_t's) and pointers to the…
shuttle87
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boost::optional vs boost::make_optional

I would like to understand better the difference between creating a boost::optional object using the default constructor: boost::optional pasta = boost::optional(spaghetti) or using the make_optional…
giubacchio
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bsoncxx::stdx::optional and mongocxx::stdx::optional

Is there any difference between bsoncxx::stdx::optional and mongocxx::stdx::optional in MongoDB C++ driver? Do they both inherit boost::optional? I can't find descriptions about them in the MongoDB C++ Driver API Documentation.
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