[Boost-users] [lambda] Making my expression less complicated

5 Sep 2008

      Hello,

In my test program below, I have a container of columns and want to output the column headers into a string separated by a tab. The lambda expression is looking fairly complicated so I wonder if it could be made simpler or if there's any other algorithm I should've used to put a separator between the elements?

Regards,

Pete

#include <algorithm>
#include <iostream>
#include <string>
#include <vector>

#include <boost/lambda/bind.hpp>
#include <boost/lambda/lambda.hpp>
#include <boost/lambda/if.hpp>

class Column
{
public:
	explicit Column(const std::string& str) : str_(str) {}
	const std::string& getColumnText() const {return str_;}
private:
	std::string str_;
};

int main()
{

	using namespace boost::lambda;
	using boost::lambda::_1;

	std::vector<Column> cols;
	cols.push_back(Column("Fred"));
	cols.push_back(Column("Jim"));
	cols.push_back(Column("Harry"));
	const std::size_t numCols = static_cast<size_t>(cols.size());

	const char fieldSeparator = '\t';

	std::string outputText;

	std::size_t i = 1;
	var_type<std::size_t>::type iV(var(i));
	std::for_each(cols.begin(),cols.end(),
		(
			var(outputText) += bind(&Column::getColumnText,_1),
			if_then(iV < constant(numCols),var(outputText) += constant(fieldSeparator)),
			++iV
		)
	);

	std::cout << '[' << outputText << ']';
}

[Boost-users] [lambda] Making my expression less complicated

Peter Barker