make D[x,y...] correspond to D[(x,y...)] for a dictionary D; see Juli…

…aLang#4803

base/dict.jl

@@ -140,6 +140,11 @@ function getindex(t::Associative, key)
     return v
 end
 
+# t[k1,k2,ks...] is syntactic sugar for t[(k1,k2,ks...)].  (Note
+# that we need to avoid dispatch loops if setindex!(t,v,k) is not defined.)
+getindex(t::Associative, k1, k2, ks...) = getindex(t, tuple(k1,k2,ks...))
+setindex!(t::Associative, v, k1, k2, ks...) = setindex!(t, v, tuple(k1,k2,ks...))
+
 push!(t::Associative, key, v) = setindex!(t, v, key)
 
 # hashing objects by identity

doc/stdlib/base.rst

@@ -642,6 +642,8 @@ Dicts can be created using a literal syntax: ``{"A"=>1, "B"=>2}``. Use of curly
 As with arrays, ``Dicts`` may be created with comprehensions. For example,
 ``{i => f(i) for i = 1:10}``.
 
+Given a dictionary ``D``, the syntax ``D[x]`` returns the value of key ``x`` (if it exists) or throws an error, and ``D[x] = y`` stores the key-value pair ``x => y`` in ``D`` (replacing any existing value for the key ``x``).  Multiple arguments to ``D[...]`` are converted to tuples; for example, the syntax ``D[x,y]``  is equivalent to ``D[(x,y)]``, i.e. it refers to the value keyed by the tuple ``(x,y)``.
+
 .. function:: Dict()
 
    ``Dict{K,V}()`` constructs a hashtable with keys of type K and values of type V.

test/collections.jl

@@ -38,6 +38,10 @@ for i=10000:20000
 end
 h = {"a" => 3}
 @test h["a"] == 3
+h["a","b"] = 4
+@test h["a","b"] == h[("a","b")] == 4
+h["a","b","c"] = 4
+@test h["a","b","c"] == h[("a","b","c")] == 4
 
 let
     z = Dict()