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Movable and move-only types supported in "out" typemaps.

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Enhance SWIGTYPE "out" typemaps to use std::move when copying
objects, thereby making use of move semantics when wrapping a function returning
by value if the returned type supports move semantics.

Wrapping functions that return move only types 'by value' now work out the box
without having to provide custom typemaps.

The implementation removed all casts in the "out" typemaps to allow the compiler to
appropriately choose calling a move constructor, where possible, otherwise a copy
constructor. The implementation alsoand required modifying SwigValueWrapper to
change a cast operator from:

  SwigValueWrapper::operator T&() const;

to

  #if __cplusplus >=201103L
    SwigValueWrapper::operator T&&() const;
  #else
    SwigValueWrapper::operator T&() const;
  #endif

This is not backwards compatible for C++11 and later when using the valuewrapper feature
if a cast is explicitly being made in user supplied "out" typemaps. Suggested change
in custom "out" typemaps for C++11 and later code:

1. Try remove the cast altogether to let the compiler use an appropriate implicit cast.
2. Change the cast, for example, from static_cast<X &> to static_cast<X &&>, using the
   __cplusplus macro if all versions of C++ need to be supported.

Issue #999
Closes #1044

More about the commit:
Added some missing "varout" typemaps for Ocaml which was falling back to
use "out" typemaps as they were missing.

Ruby std::set fix for SwigValueWrapper C++11 changes.
This commit is contained in:
William S Fulton 2022-06-22 12:52:06 +01:00
commit bf36bf7d8a
34 changed files with 508 additions and 138 deletions
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24
Doc/Manual/SWIGPlus.html
View file

@ -584,7 +584,7 @@ automatically generate a wrapper for one.
<li>
If a C++ class does not declare an explicit copy constructor, SWIG will
automatically generate a wrapper for one if the <tt>%copyctor</tt> is used.
automatically generate a wrapper for one if <tt>%copyctor</tt> is used.
</li>
<li>
@ -1352,16 +1352,19 @@ following:
<div class="code">
<pre>
Vector *wrap_cross_product(Vector *a, Vector *b) {
Vector x = *a;
Vector y = *b;
Vector r = cross_product(x, y);
Vector x;
Vector y;
Vector r;
x = *a;
y = *b;
r = cross_product(x, y);
return new Vector(r);
}</pre>
</div>
<p>
In order for the wrapper code to compile, <tt>Vector</tt> must define a copy constructor and a
default constructor.
In order for the wrapper code to compile, <tt>Vector</tt> must define a default constructor, copy assignment operator (and/or a move assignment operator for C++11 and later).
The <a href="CPlusPlus11.html#CPlusPlus11_move_only">Movable and move-only types</a> section should be read regarding C++11 move semantics and return by value.
</p>
<p>
@ -1374,9 +1377,12 @@ called the "Fulton Transform". This produces a wrapper that looks like this:
<div class="code">
<pre>
Vector cross_product(Vector *a, Vector *b) {
SwigValueWrapper&lt;Vector&gt; x = *a;
SwigValueWrapper&lt;Vector&gt; y = *b;
SwigValueWrapper&lt;Vector&gt; r = cross_product(x, y);
SwigValueWrapper&lt;Vector&gt; x;
SwigValueWrapper&lt;Vector&gt; y;
SwigValueWrapper&lt;Vector&gt; r;
x = *a;
y = *b;
r = cross_product(x, y);
return new Vector(r);
}
</pre>