Commit c1af52e4 authored by simonpj@microsoft.com's avatar simonpj@microsoft.com

Add note about overlapping instances

parent a37dfa42
......@@ -2194,8 +2194,20 @@ some other constraint. But if the instance declaration was compiled with
check for that declaration.
</para></listitem>
</itemizedlist>
All this makes it possible for a library author to design a library that relies on
overlapping instances without the library client having to know.
These rules make it possible for a library author to design a library that relies on
overlapping instances without the library client having to know.
</para>
<para>
If an instance declaration is compiled without
<option>-fallow-overlapping-instances</option>,
then that instance can never be overlapped. This could perhaps be
inconvenient. Perhaps the rule should instead say that the
<emphasis>overlapping</emphasis> instance declaration should be compiled in
this way, rather than the <emphasis>overlapped</emphasis> one. Perhaps overlap
at a usage site should be permitted regardless of how the instance declarations
are compiled, if the <option>-fallow-overlapping-instances</option> flag is
used at the usage site. (Mind you, the exact usage site can occasionally be
hard to pin down.) We are interested to receive feedback on these points.
</para>
<para>The <option>-fallow-incoherent-instances</option> flag implies the
<option>-fallow-overlapping-instances</option> flag, but not vice versa.
......
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