Why do auto and template type deduction differ for braced initializers?

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There are two important reasons for templates not to do any deduction (the two that I remember in a discussion with the guy in charge)

  • Concerns about future language extensions (there are multiple meanings you could invent – what about if we wanted to introduce perfect forwarding for braced init list function arguments?)

  • The braces can sometimes validly initialize a function parameter that is dependent

template<typename T>
void assign(T &d, const T& s);

int main() {
  vector<int> v;
  assign(v, { 1, 2, 3 });
}

If T would be deduced at the right side to initializer_list<int> but at the left side to vector<int>, this would fail to work because of a contradictional argument deduction.

The deduction for auto to initializer_list<T> is controversial. There exist a proposal for C++-after-14 to remove it (and to ban initialization with { } or {a, b}, and to make {a} deduce to the type of a).

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