CODEWITHSUNDEEP
c++c++11lambda
user2052561
user2052561

Reputation: 1339

C++ lambda return type not what expected

I'm trying to get C++11 lambdas down. I'm sure there is a way to initialize temp with a lambda (granted maybe not the best way), but I've been unable to come up with this solution.

The desired result: temp should contain an empty string for every element in data.

Here is the way I would usually initialize temp:

vector<string> temp;
for(auto i : data){
  temp.push_back("");
}

Here is the closest (I believe) that I've come to a lambda solution:

auto num = data.size();  //can't pass class members (data) to capture list
auto temp = [num](vector<string> strs) -> vector<string> {
  for(int i = 0; i < num; ++i){
    strs.push_back("");
  }
  return strs;
};

However, when I call temp.size(), I get the following error:

struct ProteinAnalyzer::convert_sequences()::__lambda0’ has no member named ‘size’ (using GCC 4.8.1)

I even explicitely declared the return type, so I'm puzzled as to why this lambda does not return vector<string>

Upvotes: 2

Views: 179

Answers (1)

user2052561
user2052561

Reputation: 1339

Thanks to the comments, I have figured out the solution to my problem. Here is how I initialized temp with a lambda function if anyone is curious:

auto num = data.size();
auto temp = [num](){
  vector<string> temp;
  for(int i = 0; i < num; ++i){
    temp.push_back("");
  }
  return temp;
}();

My problem was that I was equating the lambda with its return - two separate things.

...Although, as mentioned in the comments, vector<string> temp(data.size(), ""); is probably the best (most succint) way.

Upvotes: 1

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