ifelse is no longer a generic function

[GunnarFarneback]

JuliaLang/julia#27068 made ifelse a builtin function, so SIMD.jl can no longer add methods to it.

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julia> using SIMD
[ Info: Precompiling module SIMD
ERROR: LoadError: cannot add methods to a builtin function
Stacktrace:
 [1] top-level scope
 [2] include at ./boot.jl:314 [inlined]
 [3] include_relative(::Module, ::String) at ./loading.jl:1069
 [4] include(::Module, ::String) at ./sysimg.jl:29
 [5] top-level scope
 [6] eval at ./boot.jl:317 [inlined]
 [7] macro expansion at ./none:3 [inlined]
 [8] top-level scope at ./<missing>:0
 [9] eval(::Module, ::Any) at ./boot.jl:317
in expression starting at /home/gunnar/.julia/v0.7/SIMD/src/SIMD.jl:873
ERROR: Failed to precompile SIMD to /home/gunnar/.julia/compiled/v0.7/SIMD.ji.
Stacktrace:
 [1] error at ./error.jl:33 [inlined]
 [2] compilecache(::Base.PkgId) at ./loading.jl:1221
 [3] _require(::Base.PkgId) at ./loading.jl:1005
 [4] require(::Base.PkgId) at ./loading.jl:876
 [5] require(::Module, ::Symbol) at ./loading.jl:871

[eschnett]

Thanks for the report. Overloading ifelse this way was a corner case to begin with.

Is there also a built-in function ifelse. (with a trailing dot)? According to the new convention, this is a better name anyway, as this function acts element-wise and does not return a single Bool.

[vchuravy]

I think that runs into the same problem, since we would need to overload broadcast(::typeof(ifelse), ...)
As an alternative I would propose the name select which is commonly used in the GPU world.

[GunnarFarneback]

With regard to broadcasting I think the best option is to consider a Vec as a scalar, even if it internally holds multiple values, and be able to use broadcasting on arrays and tuples of Vec.

[GunnarFarneback]

Those who have opinions about naming now have two alternative PRs to choose from. I'm neutral about it, but note that vifelse in the short term is the easier change since select is being deprecated from Base.

[GunnarFarneback]

Resolved by #31.