Remove broadcast_elwise_op and deprecate promote_eltype_op

[martinholters]

AFAICT, broadcast_elwise_op was only used in the deprecation of _broadcast_zpreserving.

I've found the following uses of promote_eltype_op:

• ImageFiltering - only adds methods, should be no problem.
• DataArrays - actually uses Compat.promote_eltype_op.
• Compat - Defines its own version or re-exports the one from Base if it exists.

Probably the cleanest thing would be to update DataArrays not to rely on promote_eltype_op and also deprecate it in Compat. Or Compat could just use the definition from the deprecation directly.

[tkelman]

is this comment backwards?

[martinholters]

Errr... should read "so deprecate its convenience wrapper". Does that make sense?

[martinholters]

Oh, the travis i686 job failed due to

julia: /home/travis/build/JuliaLang/julia/deps/srccache/llvm-3.9.1/lib/MC/MCAsmStreamer.cpp:384: virtual void {anonymous}::MCAsmStreamer::EmitLabel(llvm::MCSymbol*): Assertion `Symbol->isUndefined() && "Cannot define a symbol twice!"' failed.
signal (6): Aborted
while loading /tmp/julia/share/julia/test/reflection.jl, in expression starting on line 43
__kernel_vsyscall at  (unknown line)
gsignal at /lib/i386-linux-gnu/libc.so.6 (unknown line)
abort at /lib/i386-linux-gnu/libc.so.6 (unknown line)
unknown function (ip: 0xf725ed14)
__assert_fail at /lib/i386-linux-gnu/libc.so.6 (unknown line)
unknown function (ip: 0xf5b57a7f)
unknown function (ip: 0xf72036bb)
unknown function (ip: 0xec83016a)
Allocations: 28517363 (Pool: 28515574; Big: 1789); GC: 21

Full log is here: https://gist.github.com/martinholters/362f5507ee7ded7b59f043c74cc52fbe

[martinholters]

Ah, that assertion failure is also what #19803 is about if I'm not mistaken, so unrelated to this PR?

[p-zubieta]

LGTM

[martinholters]

Good to go or are there any objections against this?

[TotalVerb]

Note that the existence of this function is not because of convenience, but because the suggested replacement is type-unstable. This will hammer performance of packages using this.

[TotalVerb]

It seems bad to have a type-unstable implementation, even if deprecated.

[Sacha0]

Note that the existence of this function is not because of convenience, but because the suggested replacement is type-unstable. This will hammer performance of packages using this.

Along similar lines, promote_op(f, map(eltype, As)...) is not equivalent to promote_eltype_op(f, As...) where As contains more than two arguments. A gentler deprecation might be worthwhile. Best!