"result type must be constructible from value type of input range" when creating a std::vector

Question

I have a class member that looks like this

class Controller {
    protected:
    // other stuff
    std::vector<Task<event_t, stackDepth>> taskHandlers; 

    //some more stuf
}

The Task class is non-defaultConstructible, non-copyConstructible, non-copyAssignable but is moveConstructible and moveAssignable. Everything I could read (notably, std::vector documentation) leads me to think that this should compile, but the error list looks like this (full output here) :

/usr/include/c++/9/bits/stl_uninitialized.h:127:72: error: static assertion failed: result type must be constructible from value type of input range
  127 |       static_assert(is_constructible<_ValueType2, decltype(*__first)>::value,
      |                                                                        ^~~~~

Making Task defaultConstructible did not help. The error points to the definition of the class Controller. I am using GCC 9.3.0 in c++17 mode. Did I do anything wrong ?

Fluviatile

Are you getting this error just from the single line of code you show? Is the error message the full and complete output you get? In the answer to any of those questions is "no" then please edit your question to include both the minimal reproducible example needed to reproduce the error, and also include a full and complete copy-paste of the full output. – Lorient

yes. The full output log is in the link and this line is sufficient to reproduce. – Fluviatile

@Fluviatile can you show the line in your code in what function or constructor of vector you are using ? or just point out which call in vector is giving the error ? – Aflutter

This corresponds to no call, and the error points to the beginning of the definition of the class that holds the member. Will update the question to reflect that – Fluviatile

@Fluviatile also add compiler (or stl) version – Aflutter

@Fluviatile it just "sounds like" in the error it is constructing from a range input - although i can't be sure. Are you sure you don't have anything using or operating or constructing on the vector ? I also see the number 1000000 a lot in the linked error message. It could be related or not. Again, try to figure out of which line of code is generating the error if possible. – Aflutter

I found the culprit, it was an unintended copy in an unrelated lambda which wasn't traced by the compiler. I was lucky to find it ! Thanks for the help. – Fluviatile

A proper minimal reproducible example might be helpful. – Lorient

Producing minimal reproducible examples is often more work than sorting out an issue... so then what's the point of stackoverflow? – Tidwell

@Tidwell Doing said work might mean the user figures out and resolves their own problem and then doesn't have to post it, leaving a question that has no answer except a guess... so then what's the problem with that? – Saguaro

Firstly, it is then not helpful to other users. Secondly, a guess from someone experienced can be extremely valuable. For instance when trying to produce a minimal example, it may give you a very good clue where to start looking and what part of your code you should cut out. That guess may also help other people in similar situations. – Tidwell

Answer 1

My best guess, given the current information, is that you messed up the move constructor syntax somehow - working example using just emplace_back:

The below compiles fine, link to godbolt:

#include <vector>

class X
{
public:
    X(int i) : i_(i){}
    X() = delete;
    X(const X&) = delete;
    X(X&&) = default;//change this to 'delete' will give a similar compiler error
private:
    int i_;
};


int main() { 
    std::vector<X> x;
    x.emplace_back(5);
}

Aflutter

Answer 2

This is probably not the case, but this error can also appear when the class used as a vector element inherits from an abstract class, and does not implement any of the "pure virtual" methods. And there may be no other information about this error.

Bight

Answer 3

to reproduce the error result type must be constructible from value type of input range

godbolt

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

int main() {

typedef std::vector<std::string> StrVec;

StrVec s1("a", "b"); // error
// stl_uninitialized.h:127:7: error: static_assert failed due to requirement 'is_constructible<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, const char &>::value' "result type must be constructible from value type of input range"

//StrVec s2("a", "b", "c"); // error
// error: no matching constructor for initialization of 'StrVec' (aka 'vector<basic_string<char> >')

StrVec s3({"a", "b"}); // ok
StrVec s4({"a", "b", "c"}); // ok

typedef std::vector<int> IntVec;

IntVec i1(1, 2); // silent error
for (auto i : i1) {
    std::cout << "i = " << i << '\n';
}
// silent error:
// output:
// i = 2
// expected:
// i = 1
// i = 2

//IntVec i2(1, 2, 3); // error
// error: no matching constructor for initialization of 'IntVec' (aka 'vector<int>')

IntVec i3({1, 2}); // ok
IntVec i4({1, 2, 3}); // ok

}

Shortage