Why vector<bool>::reference doesn't return reference to bool?

c++, compiler-errors, g++

Solution

Vector is specialized for bool.

It is considered a mistake of the std. Use `vector<char>` instead:

template<typename t>
struct foo {
  using type = t;
};
template<>
struct foo<bool> {
  using type = char;
};

template<typename t, typename... p>
using fixed_vector = std::vector<typename foo<t>::type, p...>;

Occasionally you may need references to a bool contained inside the vector. Unfortunately, using `vector<char>` can only give you references to chars. If you really need `bool&`, check out the Boost Containers library. It has an unspecialized version of `vector<bool>`.

Problem

``` #include <vector> struct A { void foo(){} }; template< typename T > void callIfToggled( bool v1, bool &v2, T & t ) { if ( v1 != v2 ) { v2 = v1; t.foo(); } } int main() { std::vector< bool > v= { false, true, false }; const bool f = false; A a; callIfToggled( f, v[0], a ); callIfToggled( f, v[1], a ); callIfToggled( f, v[2], a ); } ``` The compilation of the example above produces next error : ``` dk2.cpp: In function 'int main()': dk2.cpp:29:28: error: no matching function for call to 'callIfToggled(const bool&, std::vector<bool>::reference, A&)' dk2.cpp:29:28: note: candidate is: dk2.cpp:13:6: note: template<class T> void callIfToggled(bool, bool&, T&) ``` I compiled using g++ (version 4.6.1) like this : ``` g++ -O3 -std=c++0x -Wall -Wextra -pedantic dk2.cpp ``` The question is why this happens? Is `vector<bool>::reference` not `bool&`? Or is it a compiler's bug? Or, am I trying something stupid? :)

Original source