Can Spirit Parsers Be Used with `auto` Variables?

Assigning Parsers to Auto Variables

Question:

Can Spirit parsers be used with auto?

Code Snippet:

auto bracketed_z = '[' >> +qi::char_('z') >> ']';

When assigning a parser to an auto variable, as shown above, the code crashes with a segmentation fault. However, passing the parser directly to qi::parse() inline works fine.

Answer:

No, Spirit parsers are not intended to be used with auto in Spirit V2.

Explanation:

The underlying Proto expression templates hold references to temporaries. Assigning a parser to an auto variable causes the parser to be copied, which may result in dangling references.

Solutions:

To work around this issue, you can use the following methods:

• qi::copy() (available in the Boost trunk after Boost 1.55.0)
• boost::proto::deep_copy
• BOOST_SPIRIT_AUTO

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