Re: [vim/vim] E1041 is thrown when a variable is exported from a script contained in the autoload/ folder and the script is sourced more than once (Issue #19205)

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h-east left a comment (vim/vim#19205)

@mao-yining 
Why is restarting Vim a problem here?

This is not about the benefit, it is about what it costs in Vim.  A class
definition is part of the type system.  Existing objects hold a pointer to it,
member access is compiled to offsets in that definition, and the type is used
for checking at compile time.  Redefining it while objects exist means rewiring
all of that, or keeping two definitions alive at once.  That is a structural
change, not a small one, and it would affect every Vim9 script whether or not
it reloads classes.  This is where a language puts its priorities, not a matter
of the design being new or old.

Your GetInstance() table is at the right layer for this: only the script knows
which objects exist and whether they may be thrown away.  Vim cannot decide
that, throwing away an object is losing data.  It also does not remove the
cost above: functions in other scripts compiled against the class still hold
the member offsets, whether or not your table is empty.

Restarting Vim takes well under a second and has none of that risk.

You say it is still worth considering.  I do not think so.  Sorry, but this
is my last comment on this topic.

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<div style=3D"display: flex; flex-wrap: wrap; white-space: pre-wrap; align-=
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ontent.com/u/518808" /><strong>h-east</strong> left a comment <a href=3D"ht=
tps://github.com/vim/vim/issues/19205#issuecomment-5152870794">(vim/vim#192=
05)</a></div>
<p dir=3D"auto"><a class=3D"user-mention notranslate" data-hovercard-type=
=3D"user" data-hovercard-url=3D"/users/mao-yining/hovercard" data-octo-clic=
k=3D"hovercard-link-click" data-octo-dimensions=3D"link_type:self" href=3D"=
https://github.com/mao-yining">@mao-yining</a><br>
Why is restarting Vim a problem here?</p>
<p dir=3D"auto">This is not about the benefit, it is about what it costs in=
 Vim.  A class<br>
definition is part of the type system.  Existing objects hold a pointer to =
it,<br>
member access is compiled to offsets in that definition, and the type is us=
ed<br>
for checking at compile time.  Redefining it while objects exist means rewi=
ring<br>
all of that, or keeping two definitions alive at once.  That is a structura=
l<br>
change, not a small one, and it would affect every Vim9 script whether or n=
ot<br>
it reloads classes.  This is where a language puts its priorities, not a ma=
tter<br>
of the design being new or old.</p>
<p dir=3D"auto">Your GetInstance() table is at the right layer for this: on=
ly the script knows<br>
which objects exist and whether they may be thrown away.  Vim cannot decide=
<br>
that, throwing away an object is losing data.  It also does not remove the<=
br>
cost above: functions in other scripts compiled against the class still hol=
d<br>
the member offsets, whether or not your table is empty.</p>
<p dir=3D"auto">Restarting Vim takes well under a second and has none of th=
at risk.</p>
<p dir=3D"auto">You say it is still worth considering.  I do not think so. =
 Sorry, but this<br>
is my last comment on this topic.</p>

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