Static assertion failed: result type must be constructible from value type of input range

Error Explanation:

The error message “static assertion failed: result type must be constructible from value type of input range” typically occurs in C++ code. It indicates that there is an issue with the type of the result variable in relation to the input range.

Explanation and Examples:

Let’s understand this error with an example:

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

int main() {
    std::vector<int> numbers {1, 2, 3, 4, 5};
    
    // Using std::transform function incorrectly
    std::vector<bool> result;
    std::transform(numbers.begin(), numbers.end(), result.begin(), [](int num) {
        return num % 2 == 0;
    });
    
    return 0;
}

In the above code, we have a vector of numbers and we want to transform each number into a boolean value indicating whether it’s even or odd. We use the std::transform function to accomplish this. However, the error occurs because we made a mistake in providing the correct third argument for the result.

The std::transform function requires an iterator to the destination range as the third argument. It means we need to provide a range in the result vector where the transformed values will be stored. However, in the given code, we mistakenly provided the iterator result.begin() which is an invalid iterator because the result vector is empty.

To fix this error, we need to ensure that the destination range (result vector) has the capacity to store the transformed values. One way to do it is by resizing the result vector to match the size of the input range:

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

int main() {
    std::vector<int> numbers {1, 2, 3, 4, 5};
    
    // Resizing the result vector to match the input range
    std::vector<bool> result(numbers.size());
    
    // Using std::transform function correctly
    std::transform(numbers.begin(), numbers.end(), result.begin(), [](int num) {
        return num % 2 == 0;
    });
    
    // Printing the transformed values
    for (bool value : result) {
        std::cout << std::boolalpha << value << " ";
    }
    
    return 0;
}

In the updated code, we resize the result vector to match the size of the numbers vector. This ensures that the result vector has enough capacity to store the transformed values. Now, when we provide result.begin() as the third argument to std::transform, it will correctly store the transformed values in the result vector.

The output of the program will be:

false true false true false 

This indicates that the numbers 1, 3, and 5 are odd, while 2 and 4 are even.