[vtk-developers] New module system preview

[Bill Lorensen]

I will need the VTKExamples to support both api's. Also a few remote
modules.

On Mon, Oct 29, 2018, 11:18 AM Ben Boeckel <ben.boeckel at kitware.com wrote:

> On Mon, Oct 29, 2018 at 10:57:10 -0700, Bill Lorensen wrote:
> > Will I be able to support both old and new?
>
> As a consumer of modules is much easier than as a module. The variable
> names which control things are completely different (now "namespaced"
> via naming conventions). `find_package(VTK)` is similar as long as
> `VTK_LIBRARIES` was used and components are specified, but the old
> module's CMake API is gone.
>
> Old "is X enabled" detection (though this shouldn't be necessary in
> general[1]):
>
> ```cmake
> if (Module_X)
> ```
>
> New:
>
> ```cmake
> if (TARGET X)
> ```
>
> But, the module names are also different now in the new VTK as well, so
> that makes consuming harder (though predictable).
>
> Building a library used to be:
>
> ```cmake
> vtk_module_library(X ${srcs})
> ```
>
> and now has a much richer API:
>
> ```cmake
> vtk_module_add_module(X
>   SOURCES ${srcs}
>   HEADERS ${headers}
>   PRIVATE_HEADERS ${private_headers})
> ```
>
> though there is also `CLASSES` which does the de-facto standard
> `.cxx`/`.h` pairing for `SOURCES` and `HEADERS` automatically. In
> addition to the ineffectiveness of `target_*` functions on module names
> due to the kits implementation, making a module which supports both APIs
> is not going to be trivial.
>
> --Ben
>
> [1]Optional dependencies now pass `-DVTK_MODULE_ENABLE_X=` as 1 or 0 if
> available where `X` is a "safe" name for the module (basically `::`
> replaced by `_`). This is to promote `#if` rather than `#ifdef` usage
> for optional dependency detection in C++ code which triggers errors if
> present in public headers (though in consuming targets) and also
> triggers warnings if the optional dependency is removed or made
> non-optional (because the define is no longer present).
>
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