How Can I Avoid Segfaults When Using Spirit Parsers with `auto` Variables?

Avoiding Segfaults When Assigning Parsers to Auto Variables in Spirit

Spirit parsers are not inherently designed for use with auto variables in Spirit V2. This is due to underlying Proto expression templates maintaining references to temporaries.

Utilizing auto in conjunction with parsers within inline qi::parse() expressions results in successful parsing. However, assigning the parser to an auto variable and then using it in qi::parse() leads to a segfault.

To circumvent this limitation, consider the following alternatives:

• qi::copy(): Available in Spirit V2's trunk (boost_1_55_0 and later), qi::copy() can create a deep copy of the parser.
• boost::proto::deep_copy: This function enables deep copying of Proto expressions.
• BOOST_SPIRIT_AUTO: This macro, introduced in Spirit V2's discussion forums, provides a way to work with parsers in auto variables.

For further details and examples, see the following resources:

• [Spirit V2 qi bug associated with optimization level](https://stackoverflow.com/questions/12011946/spirit-v2-qi-bug-associated-with-optimization-level)
• [Spirit X3 parser within auto variable](https://stackoverflow.com/questions/27979404/spirit-x3-parser-within-auto-variable)

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