[MacPorts] #44193: qt: allow side by side installation of qt4-mac and qt5-mac

[MacPorts]

#44193: qt: allow side by side installation of qt4-mac and qt5-mac
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  Reporter:  mojca@…           |      Owner:  mcalhoun@…
      Type:  enhancement       |     Status:  new
  Priority:  Normal            |  Milestone:
 Component:  ports             |    Version:
Resolution:                    |   Keywords:
      Port:  qt4-mac, qt5-mac  |
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Comment (by rjvbertin@…):

 Replying to [comment:69 hans_meine@…]:
 > AFAIK, -no-exceptions ''was'' the default (maybe only de-facto) in the
 past, in the era of GCC 2.95 and 3.x, when it would seriously speed up
 large Qt-based projects (e.g. KDE).  However, compilers have become more
 efficient in the meantime, and more people are actually ''making use'' of
 exceptions (e.g. in the past, their use was discouraged in KDE for
 performance reasons), so the recommendation was changed.

 I have started implementing this approach after "Qt's own" Thiago Macieira
 affirmed me that it didn't change anything, and that Qt itself doesn't do
 anything with exceptions internally except in a few modules. Since those
 are an integral part of QtCore, all of QtCore is built with exceptions
 enabled in my approach. I considered going for a finer resolution, but
 decided that would be overdoing it. My change does take care that the `no-
 exceptions` setting does NOT propagate to dependents. The standard way of
 building Qt4 with `-no-exceptions` does indeed do that for some reason,
 but those changes can be reverted (see the post-destroot extract above)
 and applications using Qt can continue to use exceptions. You can imagine
 how I discovered that post-destroot bit was required, so yes, I have
 tested Qt dependent code that uses exceptions.

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Ticket URL: <https://trac.macports.org/ticket/44193#comment:70>
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