Remove try/catch block on unique_resource move constructor

[windowsair]

The clang-21 says:

include/nonstd/scope.hpp:1007:40: error:
cannot refer to a non-static member from the handler of a constructor function try block
[-Werror,-Wexceptions]
1007 | other.get_deleter()( this->get() );
| ^
1 error generated.

Since the move constructor already provides an noexcept guarantee, no exceptions will be thrown here. The try-catch block is redundant.

And a further approach is to provide a throwable exception variant of the move constructor.

[martinmoene]

There seems to be a bit more to it than providing the move constructor as:

 unique_resource( unique_resource && other )
        scope_noexcept_op(
            std11::is_nothrow_move_constructible<R1>::value && std11::is_nothrow_move_constructible<D>::value
        )
        : resource( conditional_move( std::move(other.resource), typename std11::bool_constant< std11::is_nothrow_move_assignable<R>::value >() ) )
        , deleter(  conditional_move( std::move(other.deleter ), typename std11::bool_constant< std11::is_nothrow_move_constructible<D>::value >() ) )
        , execute_on_reset( std14::exchange( other.execute_on_reset, false ) )
    {}

Proposal p0052 writes:

unique_resource(unique_resource&& rhs) noexcept (see below )

9 Effects: First, initialize resource as follows:
—(9.1) If is_nothrow_move_constructible_v<R1> is true, from std::move(rhs.resource);
—(9.2) otherwise, from rhs.resource.
[Note: If initialization of resource throws an exception, rhs is left owning the resource and will free it in due time. — end note ]
Then, initialize deleter as follows:
—(9.3) If is_nothrow_move_constructible_v<D> is true, from std::move(rhs.deleter);
—(9.4) otherwise, from rhs.deleter.
If initialization of deleter throws an exception and is_nothrow_move_constructible_v<R1> is true and rhs.execute_on_reset is true:
rhs.deleter(RESOURCE );
rhs.release();
Finally, execute_on_reset is initialized with exchange(rhs.execute_on_reset,false).

10 [Note: The explained mechanism ensures no leaking and no double release of resources. — end note ]

11 Remarks: The expression inside noexcept is equivalent to
is_nothrow_move_constructible_v<R1> && is_nothrow_move_constructible_v<D>.

[windowsair]

If my understanding is correct, the two variants below still require implementation:

// from std::move(other.resource)
unique_resource( unique_resource && other )
        scope_noexcept_op(
            std11::is_nothrow_move_constructible<R1>::value && 
            !std11::is_nothrow_move_constructible<D>::value
        ) {}

// from other.resource
unique_resource( unique_resource && other )
        scope_noexcept_op(
            !std11::is_nothrow_move_constructible<D>::value
        ) {}

[martinmoene]

Thanks @windowsair , I'll look into it (don't hold your breath :)