Throwless Variant?

[darksylinc]

ignition::rendering::Variant throws whenever it is interpreted as the wrong type.

e.g.

Variant labelAny = ogreVisual->UserData("label");
int label;
try
{
  label = std::get<int>(labelAny);
}
catch(std::bad_variant_access &e)
{
  // items with no class are considered background
  label = this->segmentationCamera->BackgroundLabel();
}

This looks fine except it makes debugging hard because "break on thrown exceptions" hits dozen/hundreds of times per frame

Desired behavior

Code should work the same as now, but could avoid throwing exceptions.

Implementation suggestion

Something like the following could work:

const int *label = std::get_if<int>(&labelAny, );
if (!label)
{
  // items with no class are considered background
  label = this->segmentationCamera->BackgroundLabel();
}

Additional context

This is a quality of life improvement for developers trying to troubleshoot a problem. IMHO exceptions should be used as a rare error that warrants attention or special handling.

What are exceptions useful for are subject to lots of debate though (e.g. Python by default treats every tiny mistake via exceptions)

[darksylinc]

If there are no objections, I can submit a PR using get_if

[iche033]

yep, no objections, we can use get_if

[azeey]

The task here is to change existing code that uses std::get to std::get_if. Examples:

• https://github.com/gazebosim/gz-rendering/blob/f3d30738726d11d240907e30699ce4c66e8a0f50/ogre2/src/Ogre2SegmentationMaterialSwitcher.cc#L91
• https://github.com/gazebosim/gz-rendering/blob/f3d30738726d11d240907e30699ce4c66e8a0f50/ogre/src/OgreThermalCamera.cc#L224
• https://github.com/gazebosim/gz-rendering/blob/f3d30738726d11d240907e30699ce4c66e8a0f50/ogre2/src/Ogre2BoundingBoxMaterialSwitcher.cc#L122