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Hi,

The is_constructible trait has problems when used on references. It will
correctly check if the construction is well formed, but that well-formed
reference construction may bind to a materialized temporary. When
is_constructible is being used to constrain "constructors" for containers
which store  references it gets the answer effectively wrong (e.g. pair,
tuple, variant?)

So I'm proposing a new is_constructible trait, one that disallows reference
binding if it constructs a temporary. The catchy name I have is:

is_constructible_and_also_doesnt_bind_a_reference_to_a_materialized_temporary

But for now lets call it 'my_is_constructible'. Below is an example of how
it functions differently from

  static_assert(is_constructible_v<int&&, long&> == true);
  static_assert(my_is_constructible_v<int&&, long&> == false);;


Maybe somebody has something better?

/Eric

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<div dir=3D"ltr"><div style=3D"font-family: arial, sans-serif; font-size: s=
mall;">Hi,</div><div style=3D"font-family: arial, sans-serif; font-size: sm=
all;"><br></div><div style=3D"font-family: arial, sans-serif; font-size: sm=
all;">The is_constructible trait has problems when used on references. It w=
ill correctly check if the construction is well formed, but that well-forme=
d reference construction may bind to a materialized temporary. When is_cons=
tructible is being used to constrain &quot;constructors&quot; for container=
s which store =C2=A0references it gets the answer effectively wrong (e.g. p=
air, tuple, variant?)=C2=A0</div><div style=3D"font-family: arial, sans-ser=
if; font-size: small;"><br></div><div style=3D"font-family: arial, sans-ser=
if; font-size: small;">So I&#39;m proposing a new is_constructible trait, o=
ne that disallows reference binding if it constructs a temporary. The catch=
y name I have is:</div><div style=3D"font-family: arial, sans-serif; font-s=
ize: small;"><br></div><div style=3D"font-family: arial, sans-serif; font-s=
ize: small;">is_constructible_and_also_<wbr>doesnt_bind_a_reference_to_a_<w=
br>materialized_temporary</div><div style=3D"font-family: arial, sans-serif=
; font-size: small;"><br></div><div style=3D"font-family: arial, sans-serif=
; font-size: small;">But for now lets call it &#39;my_is_constructible&#39;=
.. Below is an example of how it functions differently from=C2=A0</div><div =
style=3D"font-family: arial, sans-serif; font-size: small;"><br></div><div =
style=3D"font-family: arial, sans-serif; font-size: small;">=C2=A0 static_a=
ssert(is_<wbr>constructible_v&lt;int&amp;&amp;, long&amp;&gt; =3D=3D true);=
</div><div style=3D"font-family: arial, sans-serif; font-size: small;">=C2=
=A0 static_assert(my_is_<wbr>constructible_v&lt;int&amp;&amp;, long&amp;&gt=
; =3D=3D false);;</div><div style=3D"font-family: arial, sans-serif; font-s=
ize: small;"><br></div><div style=3D"font-family: arial, sans-serif; font-s=
ize: small;"><br></div><div style=3D"font-family: arial, sans-serif; font-s=
ize: small;">Maybe somebody has something better?</div><div style=3D"font-f=
amily: arial, sans-serif; font-size: small;"><br></div><div style=3D"font-f=
amily: arial, sans-serif; font-size: small;">/Eric</div></div>

<p></p>

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