Add eachindex() for AbstractStrings and Associative

There's no reason not to allow this. Fixes #11649.

base/dict.jl

@@ -192,6 +192,7 @@ in(k, v::KeyIterator) = !is(get(v.dict, k, secret_table_token),
                             secret_table_token)
 
 keys(a::Associative) = KeyIterator(a)
+eachindex(a::Associative) = KeyIterator(a)
 values(a::Associative) = ValueIterator(a)
 
 function copy(a::Associative)

base/string.jl

@@ -181,6 +181,17 @@ function chr2ind(s::AbstractString, i::Integer)
     end
 end
 
+immutable EachStringIndex{T<:AbstractString}
+    s::T
+end
+eachindex(s::AbstractString) = EachStringIndex(s)
+
+length(e::EachStringIndex) = length(e.s)
+start(e::EachStringIndex) = start(e.s)
+next(e::EachStringIndex, state) = (state, nextind(e.s, state))
+done(e::EachStringIndex, state) = done(e.s, state)
+eltype(e::EachStringIndex) = Int
+
 typealias Chars Union{Char,AbstractVector{Char},Set{Char}}
 
 function search(s::AbstractString, c::Chars, i::Integer)

doc/stdlib/arrays.rst

@@ -33,7 +33,9 @@ Basic functions
 
 .. function:: eachindex(A...)
 
-   Creates an iterable object for visiting each index of an AbstractArray ``A`` in an efficient manner. For array types that have opted into fast linear indexing (like ``Array``), this is simply the range ``1:length(A)``. For other array types, this returns a specialized Cartesian range to efficiently index into the array with indices specified for every dimension. Example for a sparse 2-d array::
+   Creates an iterable object for visiting each index of an AbstractArray ``A`` in an efficient manner. For array types that have opted into fast linear indexing (like ``Array``), this is simply the range ``1:length(A)``. For other array types, this returns a specialized Cartesian range to efficiently index into the array with indices specified for every dimension. For other iterables, including strings and dictionaries, this returns an iterator object supporting arbitrary index types (e.g. unevenly spaced or non-integer indices).
+
+   Example for a sparse 2-d array::
 
     julia> A = sprand(2, 3, 0.5)
     2x3 sparse matrix with 4 Float64 entries:

test/dict.jl

@@ -333,3 +333,8 @@ let d = Dict{Int,Int}()
     end
     @test length(d) == 1
 end
+
+# iteration
+d = Dict('a'=>1, 'b'=>1, 'c'=> 3)
+@test [d[k] for k in keys(d)] == [d[k] for k in eachindex(d)] ==
+      [v for (k, v) in d] == [d[x[1]] for (i, x) in enumerate(d)]

test/strings.jl

@@ -1892,3 +1892,8 @@ end
 @test_throws BoundsError Base.checkstring(b"abcdef", 3, 0)
 @test_throws BoundsError Base.checkstring(b"abcdef", 3, 7)
 @test_throws ArgumentError Base.checkstring(b"abcdef", 3, 1)
+
+# iteration
+@test [c for c in "ḟøøƀäṙ"] == ['ḟ', 'ø', 'ø', 'ƀ', 'ä', 'ṙ']
+@test [i for i in eachindex("ḟøøƀäṙ")] == [1, 4, 6, 8, 10, 12]
+@test [x for x in enumerate("ḟøøƀäṙ")] == [(1, 'ḟ'), (2, 'ø'), (3, 'ø'), (4, 'ƀ'), (5, 'ä'), (6, 'ṙ')]