Constructing a value through two implicit constructors?

Question

TLDR: I have two templatized classes Outer and Inner. Inner can be implicitly constructed from X

Answer 1

Your first example requires two user defined conversions to compile — SomeType -> Inner -> Outer. However, at most one user defined conversion can be applied implicitly.

Quoting N3337, §12.3 [class.conv]

1   Type conversions of class objects can be specified by constructors and by conversion functions. These conversions are called user-defined conversions and are used for implicit type conversions (Clause 4), for initialization (8.5), and for explicit type conversions (5.4, 5.2.9).

4   At most one user-defined conversion (constructor or conversion function) is implicitly applied to a single value.

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If the goal is to avoid having to mention Inner<SomeType> in the return statement, you can use list initialization.

Outer<Inner<SomeType>> DoSomethingWorks2() {
  SomeType value;
  return {std::move(value)};
}