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Nicola Musatti · Guest

In the latest available draft standard (N2134) § 17.4.3.6
[res.on.functions] states:

1 In certain cases (replacement functions, handler functions,
operations on
types used to instantiate standard library template components), the
C++
Standard Library depends on components supplied by a C++ program. If
these components do not meet their requirements, the Standard places
no
requirements on the implementation.
2 In particular, the effects are undefined in the following cases:

[...]

- if an incomplete type (3.9) is used as a template argument when
instantiating a template component.

This is contradicted by § 20.6.6.2/2 [util.smartptr.shared] which
states:

[...]

The template parameter T of shared_ptr may be an incomplete type.

The last bullet of § 17.4.3.6/2 should be modified to allow for
exceptions, as in:

- if an incomplete type (3.9) is used as a template argument when
instantiating a template component, unless explicitly specified
otherwise.

Cheers,
Nicola Musatti

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