What prevents adding the 64-bit Windows platform to VCL component packages?

Question

With most Delphi and C++ Builder projects, including component packages, you can add a 64-bit Windows target by right-clicking on the Target Platforms item in the Project Manager and selecting Add Platform, then choosing '64-bit Windows' in the resulting dialog.

Recently while installing components in a new installation of RAD Studio XE4, I've been unable to do this for some components. For example:

This specific example is TMS's Advanced Poly List, but it's happened for other component packages as well - but not all. Some have the target available, and for those I can build the package and create a 64-bit VCL forms application that uses the component fine.

What is preventing the Win64 target appearing in the dialog, and how can I re-enable it?

Answer 1

In C++ Builder XE6, released a few days ago (mid-April 2014), you can now create 64-bit packages in C++.

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Old outdated answer (valid for C++ Builder XE3, 4 and 5):

64-bit compilation is a missing feature for C++ packages in XE3 and XE4.

For Delphi, you can target Win32, Win64, OSX and (I think) iOS for packages.

For C++, you can only target Win32 and OSX, even if you have the 64-bit compiler installed. This is documented for XE3, and is apparently not fixed in XE4 either.

There was no QC report for this, so I have added one. Please feel free to vote for it. My rationale for its importance is that packages are an important part of the Delphi / VCL ecosystem, especially for components. While you can use Delphi-created 64-bit packages in your 64-bit C++ project, this means you can't use components written in C++ in a 64-bit program. For us, this will require rewriting our components in Delphi, or waiting until the compiler supports it.