Provide a more useful error message for calling map on a Dict with a …

…non-Pair return type
JuliaLang · Aug 13, 2016 · eb95919 · eb95919
1 parent b066714
commit eb95919
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diff --git a/base/dict.jl b/base/dict.jl
@@ -848,3 +848,6 @@ function similar(t::ImmutableDict)
     end
     return t
 end
+
+_similar_for{P<:Pair}(c::Dict, ::Type{P}, itr, isz) = similar(c, P)
+_similar_for(c::Associative, T, itr, isz) = throw(ArgumentError("for Associatives, similar requires an element type of Pair;\n  if calling map, consider a comprehension instead"))
diff --git a/test/dict.jl b/test/dict.jl
@@ -388,6 +388,11 @@ 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)]
 
+# generators, similar
+d = Dict(:a=>"a")
+@test @inferred(map(identity, d)) == d
+@test @inferred(map(p->p.first=>p.second[1], d)) == Dict(:a=>'a')
+@test_throws ArgumentError map(p->p.second, d)
 
 # Issue 12451
 @test_throws ArgumentError Dict(0)