bogous

[hooshdar3]

Hi.
Isn't this class definition

class WordCounter : public Mapper {
public:
virtual void Map(const MapInput& input) {
const string& text = input.value();
const int n = text.size();
for (int i = 0; i < n; ) {
// Skip past leading whitespace
while ((i < n) && isspace(text[i]))
i++;
// Find word end
int start = i;
while ((i < n) && !isspace(text[i]))
i++;
if (start < i)
Emit(text.substr(start,i-start),"1");
}
}
};
REGISTER_MAPPER(WordCounter);
// User’s reduce function
class Adder : public Reducer {
virtual void Reduce(ReduceInput* input) {
/ Iterate over all entries with the
// same key and add the values
int64 value = 0;
while (!input->done()) {
value += StringToInt(input->value());
input->NextValue();
}
// Emit sum for input->key()
Emit(IntToString(value));
}
};
REGISTER_REDUCER(Adder);
int main(int argc, char** argv) {
ParseCommandLineFlags(argc, argv);
MapReduceSpecification spec;
// Store list of input files into "spec"
for (int i = 1; i < argc; i++) {
MapReduceInput* input = spec.add_input();
input->set_format("text");
input->set_filepattern(argv[i]);
input->set_mapper_class("WordCounter");
}

/ Specify the output files:
//
/gfs/test/freq-00000-of-00100
//
/gfs/test/freq-00001-of-00100
//
...
MapReduceOutput* out = spec.output();
out->set_filebase("/gfs/test/freq");
out->set_num_tasks(100);
out->set_format("text");
out->set_reducer_class("Adder");

// Optional: do partial sums within map
// tasks to save network bandwidth
out->set_combiner_class("Adder");

// Tuning parameters: use at most 2000
// machines and 100 MB of memory per task
spec.set_machines(2000);
spec.set_map_megabyte

How cab const string& text be assigned something?

Thanks in advance

[JLBorges]

> How cab const string& text be assigned something?

In line 4: const string& text = input.value();

the = does not stand for assignment; it is reference initialization The type of text is 'reference to const string', in the initialization, the reference is being bound to an object of type string.
http://en.cppreference.com/w/cpp/language/reference_initialization