Cannot return non_const reference to contained value for uninitialized optional variable type.

Open
#111 2 comments 0 reactions 0 assignees View on GitHub

Nobody has claimed this yet.

Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
30/100
Issue type
Feature
Clarity
Needs clarification
Activity status
Stale
Tech stack
cpp
Domain
backend

Research direction

Start with boost/optional.hpp lines 1267-1281 and inspect the non-const get(), get_value_or(), and operator->() implementations and their BOOST_ASSERT checks. Review the serialization-library use case described in the issue and determine the intended behavior for an uninitialized optional; the work is done when that behavior is resolved and covered appropriately.

Written by the indexing model from the issue text.

Description

I'm having an issue with the following code:

From boost/optional.hpp - lines 1267-1281 (problem lines marked with ~)

// Returns a reference to the value if this is initialized, otherwise,
// the behaviour is UNDEFINED
// No-throw
reference_const_type get() const { BOOST_ASSERT(this->is_initialized()) ; return this->get_impl(); }
~ reference_type get() { BOOST_ASSERT(this->is_initialized()) ; return this->get_impl(); }

/// Returns a copy of the value if this is initialized, 'v' otherwise
reference_const_type get_value_or ( reference_const_type v ) const { return this->is_initialized() ? get() : v ; }
reference_type get_value_or ( reference_type v ) { return this->is_initialized() ? get() : v ; }

/// Returns a pointer to the value if this is initialized, otherwise,
// the behaviour is UNDEFINED
// No-throw
pointer_const_type operator->() const { BOOST_ASSERT(this->is_initialized()) ; return this->get_ptr_impl() ; }
~ pointer_type operator->() { BOOST_ASSERT(this->is_initialized()) ; return this->get_ptr_impl() ; }

The code returns non-const reference and pointer. These used for getting a reference to the contained variable holding the type presumably so it can be modified. (this is my case). BUT, the BOOST_ASSERT traps if the variable isn't initialized. This makes it impossible to modify the contained value. The is necessary in the context of the serialization library.

Dominant language
C++
Stars
60
Forks
75
No merged PRs in 30d

Contributor guide

No contributing guide indexed for this repository

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from boostorg/optional

All issues in boostorg/optional

Similar issues

More C++ issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.