Brace Enclosed Initializer List? convert to vector

Question

so I have a piece of code that I am attempting to test. The code is checking that a few vectors (these are elements of structs) are equivalent to known vectors at certain points, however I am running into an issue. When I attempt to compare the vector to the known vector as follows,

assert((class1.getattr().getattr().getVec(key) == {4,3,2,2}))

I get the following error:

assertAll.cpp:105:82: error: could not convert ‘{4,3,2,2}’ from ‘<brace-enclosed initializer list>’ to ‘std::vector<int>’

the rest of the code is all correct, and the lval of the assert is definitely a vector as it should be. I am compiling with the flags, -std=c++11 -Wall -Wextra -pedantic -O in g++. Does anybody know how to fix this? Is there a way to typecast the bracket enclosed initializer list to a vector, or is there a better way to do this?

You could write a small function that compares vectors element by element and then return a bool value that could be checked using assert or use std::equal. — learningToCode, Dec 06 '14 at 02:03
the problem is that cpp does not recognize the bracketed information as vectors, and therefore any function that uses std::vector will not work on it. — Eric, Dec 06 '14 at 02:06
our first thought was to pass it to a compare function as well, but as we cannot type cast the second part as a vector apparently that did not work either. — Eric, Dec 06 '14 at 02:08
It is possible that this is grammatically forbidden. In fact, clang++ says *"error: initializer list cannot be used on the right hand side of operator '=='"* and I cannot find a way to produce this expression with the grammar summary. Several expressions explicitly allow braced-init-lists, such as subscription (directly) and assignment (via initializer-clause). — dyp, Dec 06 '14 at 02:32

cartographer · Accepted Answer · 2014-12-06T02:30:03.083

Does anybody know how to fix this? Is there a way to typecast the bracket enclosed initializer list to a vector

Interestingly, I get a completely different error on Clang 3.5 and GCC 4.9.2 when I try something similar, but you can just use the initializer list syntax to construct a vector in place (not quite typecasting, I guess):

assert((class1.getattr().getattr().getVec(key) == std::vector<int>{4,3,2,2}))

I'm not sure how to do that thing where you can run code on Coliru and such, but the following code works for me on GCC 4.9.2 using g++ -std=c++11 -Wall -pedantic

#include <cassert>
#include <vector>

std::vector<int> foo() {
    return {1,2,3,4};
}

template<class T>
bool is_equal(const T& a, const T& b) {
    return a == b;
}

int main()
{
    assert((foo() == std::vector<int>{1,2,3,4}));

    assert(is_equal(foo(), {1,2,3,4}));

    assert([&](std::vector<int> v) -> bool {
        return foo() == v;
    }({1,2,3,4}));
}

Granted, nobody in their right mind would use a lambda like that, but as you might be able to tell from the examples, you basically just need to tell the compiler that the two sides are the same type in order to get it to convert the initializer list to a vector.

that does not solve the issue, and I also tried that. – Eric Dec 06 '14 at 02:13 — Eric, Dec 06 '14 at 02:13

Brace Enclosed Initializer List? convert to vector

1 Answers1