Item 6: Use the Explicitly Typed Initializer Idiom When auto Deduces Undesired Types
General rule: “Invisible” proxy classes don’t play well with auto.
Use explicitly typed initializer idiom to work around it.
// This might not be a great way of using std::vector,
// but this is just an example...
std::vector<bool> foo();
// Surprise! x is not bool-typed,
// but std::vector<bool>::reference -typed
// that reference to a temporary vector object
// (dangling pointer!)
auto x = foo()[5];
This example might be artificial, but accessing a proxy object that is referencing to a temporary object is not rare.
// Explicitly typed initializer idiom
// Emphasize you make this cast deliberately
auto x = static_cast<bool>(foo()[5]);
