The wording for the specification of facilities that propagate exceptions inadvertently exclude some cases of thrown exceptions. The ones I've identified have the form "any exception thrown by the {(selected) constructor,construction} of {T,some object}". This formulation excludes exceptions thrown by the initialization of the constructor's parameters ([expr.call] p7). These are not thrown by the constructor nor during the construction of the object (after its construction has begun ([class.cdtor] p1)).
Implying that the initialization of the constructor's parameter are part of the effects for which exceptions are propagated can be done with these changes:
T.T,some object}".The former is already present in the standard, as exemplified below. As for the latter (emphasis mine),
Examples Example, goodThe process of initialization described in [dcl.init] applies to all initializations regardless of syntactic context, including the initialization of a function parameter ([expr.call]), the initialization of a return value ([stmt.return]), or when an initializer follows a declarator.
-- https://eel.is/c++draft/dcl.init p1
Constructors and member functions of pair do not throw exceptions unless one of the element-wise operations specified to be called for that operation throws an exception. -- https://eel.is/c++draft/pairs.pair#1
Talking in terms of operations includes initialization.
Example, badFor each tuple constructor, an exception is thrown only if the construction of one of the types in Types throws an exception. -- https://eel.is/c++draft/tuple.cnstr#2
We can make a tuple constructor throw an exception other than by constructing one of the specified types: https://godbolt.org/z/enGThMq4P.
#include <tuple>
struct X { X(int) { } };
struct Y { operator int() { throw 0; } };
int main() { std::tuple<X>(Y{}); }
As described at the top, this throws before beginning the construction of an X subobject.
Do note that the constructor above is described to initialize:
Effects: Initializes the elements in the tuple with the corresponding value in std::forward(u). -- https://eel.is/c++draft/tuple.cnstr#13
One could argue that [tuple.cnstr] doesn't say "if and only if". That just leaves in the air what happens in this case.
Example, goodThrows: Any exception thrown by the initialization of the selected alternative Tj. -- https://eel.is/c++draft/variant.ctor#18
Throws: Any exception thrown by calling the selected constructor of T. -- https://eel.is/c++draft/variant.ctor#23
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