faster copy! between arrays of different types (ref JuliaLang#11004)

base/abstractarray.jl

@@ -211,6 +211,8 @@ end
 
 squeeze(A::AbstractArray, dim::Integer) = squeeze(A, (Int(dim),))
 
+## from general iterable to any array
+
 function copy!(dest::AbstractArray, src)
  i = 1
  for x in src
@@ -220,7 +222,6 @@ function copy!(dest::AbstractArray, src)
  return dest
 end
 
-# copy with minimal requirements on src
 # if src is not an AbstractArray, moving to the offset might be O(n)
 function copy!(dest::AbstractArray, doffs::Integer, src)
  doffs < 1 && throw(BoundsError())
@@ -247,7 +248,7 @@ function copy!(dest::AbstractArray, doffs::Integer, src, soffs::Integer)
  dn = done(src, st)
  dn && throw(BoundsError())
  i, dmax = doffs, length(dest)
- @inbounds while !dn
+  @inbounds while !dn
  i > dmax && throw(BoundsError())
  val, st = next(src, st)
  dest[i] = val
@@ -280,7 +281,20 @@ function copy!(dest::AbstractArray, doffs::Integer, src, soffs::Integer, n::Inte
  return dest
 end
 
-# if src is an AbstractArray and a source offset is passed, use indexing
+## copy between abstract arrays - generally more efficient
+## since a single index variable can be used.
+
+function copy!(dest::AbstractArray, src::AbstractArray)
+ n = length(src)
+ if n > length(dest)
+ throw(BoundsError())
+ end
+ @inbounds for i = 1:n
+ dest[i] = src[i]
+ end
+ return dest
+end
+
 function copy!(dest::AbstractArray, doffs::Integer, src::AbstractArray)
  copy!(dest, doffs, src, 1, length(src))
 end