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Errors concerning 'NSString' or other Foundation classes encountered in client project which includes iOS sample files (VisageRendering.cpp, etc.)?
It is necessary to make sure that VisageRendering.cpp is compiled as an Objective-C++ source, and not as a C++ source by changing 'Type' property of the file on the right-hand property side in the Xcode editor. This applies generally to any source which includes/imports (directly or indirectly) any Apple classes.
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