Got stuck porting legacy boost::spirit code - c++

Question

I am porting some legacy code from VS2010 & boost1.53 to VS2017 & boost1.71.
I have got stuck last two hours while trying compiling it.
The code is:
#include <string>
#include <vector>
#include <fstream>
#include <boost/config/warning_disable.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
namespace qi = boost::spirit::qi;
using qi::_1; using qi::_2; using qi::_3; using qi::_4;
enum TYPE { SEND, CHECK, COMMENT };
struct Command
{
TYPE type;
std::string id;
std::string arg1;
std::string arg2;
bool checking;
};
class Parser
{
typedef boost::spirit::istream_iterator It;
typedef std::vector<Command> Commands;
struct deferred_fill
{
template <typename R, typename S, typename T, typename U> struct result { typedef void type; };//Not really sure still necessary
typedef void result_type;//Not really sure still necessary
void operator() (boost::iterator_range<It> const& id, boost::iterator_range<It> const& arg1, bool checking, Command& command) const
{
command.type = TYPE::SEND;
command.id.assign(id.begin(), id.end());
command.arg1.assign(arg1.begin(), arg1.end());
command.checking = checking;
}
};
private:
qi::symbols<char, bool> value;
qi::rule<It> ignore;
qi::rule<It, Command()> send;
qi::rule<It, Commands()> start;
boost::phoenix::function<deferred_fill> fill;
public:
std::vector<Command> commands;
Parser()
{
using namespace qi;
using boost::phoenix::push_back;
value.add("TRUE", true)
("FALSE", false);
send = ("SEND_CONFIRM" >> *blank >> '(' >> *blank >> raw[*~char_(',')] >> ','
>> *blank >> raw[*~char_(',')] >> ','
>> *blank >> value >> *blank >> ')' >> *blank >> ';')[fill(_1, _2, _3, _val)];
ignore = *~char_("\r\n");
start = (send[push_back(_val, _1)] | ignore) % eol;
}
void parse(const std::string& path)
{
std::ifstream in(path, std::ios_base::in);
if (!in) return;
in >> std::noskipws;//No white space skipping
boost::spirit::istream_iterator first(in);
boost::spirit::istream_iterator last;
qi::parse(first, last, start, commands);
}
};
int main(int argc, char* argv[])
{
Parser parser;
parser.parse("file.txt");
return 0;
}
The compiler complains in the next way (only copy first lines):
1>z:\externos\boost_1_71_0\boost\phoenix\core\detail\function_eval.hpp(116): error C2039: 'type': no es un miembro de 'boost::result_of<const Parser::deferred_fill (std::vector<Value,std::allocator<char>> &,std::vector<Value,std::allocator<char>> &,boost::iterator_range<Parser::It> &,Command &)>'
1> with
1> [
1> Value=char
1> ]
1>z:\externos\boost_1_71_0\boost\phoenix\core\detail\function_eval.hpp(114): note: vea la declaración de 'boost::result_of<const Parser::deferred_fill (std::vector<Value,std::allocator<char>> &,std::vector<Value,std::allocator<char>> &,boost::iterator_range<Parser::It> &,Command &)>'
1> with
1> [
1> Value=char
1> ]
1>z:\externos\boost_1_71_0\boost\phoenix\core\detail\function_eval.hpp(89): note: vea la referencia a la creación de instancias de plantilla clase de 'boost::phoenix::detail::function_eval::result_impl<F,void (Head,const boost::phoenix::actor<boost::spirit::argument<1>>&,const boost::phoenix::actor<boost::spirit::argument<2>>&,const boost::phoenix::actor<boost::spirit::attribute<0>>&),const boost::phoenix::vector2<Env,Actions> &>' que se está compilando
1> with
1> [
1> F=const boost::proto::exprns_::basic_expr<boost::proto::tagns_::tag::terminal,boost::proto::argsns_::term<Parser::deferred_fill>,0> &,
1> Head=const boost::phoenix::actor<boost::spirit::argument<0>> &,
1> Env=boost::phoenix::vector4<const boost::phoenix::actor<boost::proto::exprns_::basic_expr<boost::phoenix::detail::tag::function_eval,boost::proto::argsns_::list5<boost::proto::exprns_::basic_expr<boost::proto::tagns_::tag::terminal,boost::proto::argsns_::term<Parser::deferred_fill>,0>,boost::phoenix::actor<boost::spirit::argument<0>>,boost::phoenix::actor<boost::spirit::argument<1>>,boost::phoenix::actor<boost::spirit::argument<2>>,boost::phoenix::actor<boost::spirit::attribute<0>>>,5>> *,boost::fusion::vector<std::vector<char,std::allocator<char>>,std::vector<char,std::allocator<char>>,boost::iterator_range<Parser::It>,std::vector<char,std::allocator<char>>,boost::iterator_range<Parser::It>,std::vector<char,std::allocator<char>>,bool,std::vector<char,std::allocator<char>>,std::vector<char,std::allocator<char>>> &,boost::spirit::context<boost::fusion::cons<Command &,boost::fusion::nil_>,boost::fusion::vector<>> &,bool &> &,
1> Actions=const boost::phoenix::default_actions &
1> ]
I guess that error is related with the use of boost::spirit::istream_iterator, instead of char*, but I cann't figure out how to fix it to work again.
I have run out of ideas, please, anyone can see where my mistake is?

Answer 1

Aw. You're doing awesome things. Sadly/fortunately it's overcomplicated.
So let's first fix, and then simplify.
The Error
It's like you said,
void operator() (boost::iterator_range<It> const& id, boost::iterator_range<It> const& arg1, bool checking, Command& command) const
Doesn't match what actually gets invoked:
void Parser::deferred_fill::operator()(T&& ...) const [with T =
{std::vector<char>&, std::vector<char>&,
boost::iterator_range<boost::spirit::basic_istream_iterator<...> >&,
Command&}]
The reason is NOT the iterator (as you can see it's boost::spirit__istream_iterator alright).
However it's because you're getting other things as attributes. Turns out *blank exposes the attribute as a vector<char>. So you can "fix" that by omit[]-ing those. Let's instead wrap it in an attribute-less rule like ignore so we reduce the clutter.
Now the invocation is with
void Parser::deferred_fill::operator()(T&& ...) const [with T = {boost::iterator_range<It>&, boost::iterator_range<It>&, bool&, Command&}]
So it is compatible and compiles. Parsing:
SEND_CONFIRM("this is the id part", "this is arg1", TRUE);
With
Parser parser;
parser.parse("file.txt");
std::cout << std::boolalpha;
for (auto& cmd : parser.commands) {
std::cout << '{' << cmd.id << ", "
<< cmd.arg1 << ", "
<< cmd.arg2 << ", "
<< cmd.checking << "}\n";
}
Prints
{"this is the id part", "this is arg1", , TRUE}
Let's improve this
This calls for a skipper
This calls for automatic attribute propagation
Some other elements of style
Skippers
Instead of "calling" a skipper explicitly, let's use the built in capability:
rule<It, Attr(), Skipper> x;
defines a rule that skips over inputs sequences matched by a parser of the Skipper type. You need to actually pass in the skipper of that type.
using qi::phrase_parse instead of qi::parse
by using the qi::skip() directive
I always advocate the second approach, because it makes for a friendlier, less error-prone interface.
So declaring the skipper type:
qi::rule<It, Command(), qi::blank_type> send;
We can reduce the rule to:
send = (lit("SEND_CONFIRM") >> '('
>> raw[*~char_(',')] >> ','
>> raw[*~char_(',')] >> ','
>> value >> ')' >> ';')
[fill(_1, _2, _3, _val)];
And than pass a skipper from the start rule:
start = skip(blank) [
(send[push_back(_val, _1)] | ignore) % eol
];
That's all. Still compiles and matches the same.
Live On Coliru
Skipping with Lexemes
Still the same topic, lexemes actually inhibit the skipper¹, so you don't have to raw[]. This changes the exposed attributes to vector<char> as well:
void operator() (std::vector<char> const& id, std::vector<char> const& arg1, bool checking, Command& command) const
Live On Coliru
Automatic Attribute Propagation
Qi has semantic actions, but its real strength is in them being optional: Boost Spirit: "Semantic actions are evil"?
push_back(_val, _1) is actually the automatic attribute propagation semantics anwyays for *p, +p and p % delim² anyways, so just drop it:
start = skip(blank) [
(send | ignore) % eol
];
(note that send|ignore actually synthesizes optional<Command> which is fine for automatic propagation)
std::vector is attribute-compatible with std::string, e.g.. So if we can add a placeholder for arg2 we can match the Command structure layout:
send = lit("SEND_CONFIRM") >> '('
>> attr(SEND) // fill type
>> lexeme[*~char_(',')] >> ','
>> lexeme[*~char_(',')] >> ','
>> attr(std::string()) // fill for arg2
>> value >> ')' >> ';'
;
Now to be able to drop fill and its implementation, we have to adapt Command as a fusion sequence:
BOOST_FUSION_ADAPT_STRUCT(Command, type, id, arg1, arg2, checking)
Elements of Style 1
Using a namespace for your Command types makes it easier to ADL use the operator<< overloads for Commands, se we can just std::cout << cmd;
At this point, it all works in a fraction of the code: Live On Coliru
Elements of Style 2
If you can, make your parser stateless. That means it can be const, so you can:
reuse it without costly construction
the optimizer has more to work with
it's more testable (stateful things are harder to prove idempotent)
So, instead of having commands a member, just return them. While we're at it, we can make parse a static function
Instead of hardcoding the iterator type, it's flexible to have it as a template argument. That way you're not stuck with the overhead of multi_pass_adaptor and istream_iterator if you have a command in a char[] buffer, string or string_view at some point.
Also, deriving your Parser from qi::grammar with a suitable entry-point means you can use it as a parser expression (actually a non-terminal, just like rule<>) as any other parser.
Consider enabling rule debugging (see example)
Full Code
Live On Coliru
#define BOOST_SPIRIT_DEBUG
#include <boost/spirit/include/qi.hpp>
#include <fstream>
namespace qi = boost::spirit::qi;
namespace Commands {
enum TYPE { SEND, CHECK, COMMENT };
enum BOOL { FALSE, TRUE };
struct Command {
TYPE type;
std::string id;
std::string arg1;
std::string arg2;
BOOL checking;
};
typedef std::vector<Command> Commands;
// for (debug) output
static inline std::ostream& operator<<(std::ostream& os, TYPE t) {
switch (t) {
case SEND: return os << "SEND";
case CHECK: return os << "CHECK";
case COMMENT: return os << "COMMENT";
}
return os << "(unknown)";
}
static inline std::ostream& operator<<(std::ostream& os, BOOL b) {
return os << (b?"TRUE":"FALSE");
}
using boost::fusion::operator<<;
}
BOOST_FUSION_ADAPT_STRUCT(Commands::Command, type, id, arg1, arg2, checking)
namespace Commands {
template <typename It>
class Parser : public qi::grammar<It, Commands()> {
public:
Commands commands;
Parser() : Parser::base_type(start) {
using namespace qi;
value.add("TRUE", TRUE)
("FALSE", FALSE);
send = lit("SEND_CONFIRM") >> '('
>> attr(SEND) // fill type
>> lexeme[*~char_(',')] >> ','
>> lexeme[*~char_(',')] >> ','
>> attr(std::string()) // fill for arg2
>> value >> ')' >> ';'
;
ignore = +~char_("\r\n");
start = skip(blank) [
(send | ignore) % eol
];
BOOST_SPIRIT_DEBUG_NODES((start)(send)(ignore))
}
private:
qi::symbols<char, BOOL> value;
qi::rule<It> ignore;
qi::rule<It, Command(), qi::blank_type> send;
qi::rule<It, Commands()> start;
};
static Commands parse(std::istream& in) {
using It = boost::spirit::istream_iterator;
static const Parser<It> parser;
It first(in >> std::noskipws), //No white space skipping
last;
Commands commands;
if (!qi::parse(first, last, parser, commands)) {
throw std::runtime_error("command parse error");
}
return commands; // c++11 move semantics
}
}
int main() {
try {
for (auto& cmd : Commands::parse(std::cin))
std::cout << cmd << "\n";
} catch(std::exception const& e) {
std::cout << e.what() << "\n";
}
}
Prints
(SEND "this is the id part" "this is arg1" TRUE)
Or indeed with BOOST_SPIRIT_DEBUG defined:
<start>
<try>SEND_CONFIRM("this i</try>
<send>
<try>SEND_CONFIRM("this i</try>
<success>\n</success>
<attributes>[[SEND, [", t, h, i, s, , i, s, , t, h, e, , i, d, , p, a, r, t, "], [", t, h, i, s, , i, s, , a, r, g, 1, "], [], TRUE]]</attributes>
</send>
<send>
<try></try>
<fail/>
</send>
<ignore>
<try></try>
<fail/>
</ignore>
<success>\n</success>
<attributes>[[[SEND, [", t, h, i, s, , i, s, , t, h, e, , i, d, , p, a, r, t, "], [", t, h, i, s, , i, s, , a, r, g, 1, "], [], TRUE]]]</attributes>
</start>
¹ while pre-skipping as you require; see Boost spirit skipper issues
² (and then some, but let's not digress)