Type deduction in C++ has evolved significantly. The auto keyword (since C++11) is the most prominent feature, allowing the compiler to deduce the type of a variable from its initializer.
Type Deduction Rules
The rules for auto are virtually identical to template type deduction. However, auto deduction treats braced-init-lists as std::initializer_list, which template deduction does not.
auto x = 27; // x is int
const auto cx = x; // cx is const int
const auto& rx = x; // rx is const int&Decltype(auto) (C++14)
While auto follows template deduction (and thus strips away references and top-level const), decltype(auto) deduces the exact type including references.
int x = 0;
int& getRef() { return x; }
auto a = getRef(); // a is int (copy)
decltype(auto) b = getRef(); // b is int& (reference)Generic Lambdas (C++14)
You can use auto in lambda parameters to create generic lambdas.
auto adder = [](auto a, auto b) { return a + b; };
adder(5, 10); // int version
adder(1.5, 2.0); // double version