Add docs, do-block function for get!

base/dict.jl

@@ -529,6 +529,21 @@ function get!{K,V}(h::Dict{K,V}, key0, default)
     return v
 end
 
+function get!{K,V}(default::Function, h::Dict{K,V}, key0)
+    key = convert(K,key0)
+    if !isequal(key,key0)
+        error(key0, " is not a valid key for type ", K)
+    end
+
+    index = ht_keyindex2(h, key)
+
+    index > 0 && return h.vals[index]
+
+    v = convert(V,  default())
+    _setindex!(h, v, key, -index)
+    return v
+end
+
 function getindex{K,V}(h::Dict{K,V}, key)
     index = ht_keyindex(h, key)
     return (index<0) ? throw(KeyError(key)) : h.vals[index]::V

doc/stdlib/base.rst

@@ -727,6 +727,21 @@ Given a dictionary ``D``, the syntax ``D[x]`` returns the value of key ``x`` (if
 
    Return the value stored for the given key, or the given default value if no mapping for the key is present.
 
+.. function:: get!(collection, key, default)
+
+   Return the value stored for the given key, or if no mapping for the key is present, store ``key => default``, and return ``default``.
+
+.. function:: get!(f::Function, collection, key)
+
+   Return the value stored for the given key, or if no mapping for the key is present, store ``key => f()``, and return ``f()``.
+
+   This is intended to be called using ``do`` block syntax::
+
+     get!(dict, key) do
+         # default value calculated here
+	 time()
+     end
+
 .. function:: getkey(collection, key, default)
 
    Return the key matching argument ``key`` if one exists in ``collection``, otherwise return ``default``.

test/collections.jl

@@ -154,7 +154,10 @@ let
     def = {}
     @test get!(d, 8, 5) == 19
     @test get!(d, 19, 2) == 2
-    @test d == {8=>19, 19=>2}
+    @test get!(d, 42) do
+        int(e^2)
+    end == 7
+    @test d == {8=>19, 19=>2, 42=>7}
 end
 
 # issue #2540