There is no conversion from Pair to Tuple. The construction: (a, b, c) = d
works for any iterable collection d. The same holds for the for loop construction. There used to be a type inference issue, but I fixed it in https://github.com/JuliaLang/julia/pull/12493. The output of code_warntype is a little wonky but you can see it knows the types of k and v here: s1 = (Base.box)(Base.Int,(Base.add_int)(s1::Int64,k::Int64)::Any):: Int64 # none, line 7: s2 = (Base.box)(Base.Float64,(Base.add_float)(s2::Float64,v::Float64 )::Any)::Float64 The LLVM IR also indicates it's being optimized correctly. Simon On Tuesday, September 8, 2015 at 10:10:21 AM UTC-4, vav...@uwaterloo.ca wrote: > > The following code loops over a Dict: > > function test_paircvt1() > d = Dict(1=>5.5, 3=>-2.2) > s1 = 0 > s2 = 0.0 > for (k,v) in d > s1 += k > s2 += v > end > s1, s2 > end > > Two issues to ask about: > > (1) Since eltype(d)==Pair{Int,Float64}, Julia is automatically converting > Pair{Int,Float64} to Tuple{Int,Float64}. How is this done? I looked for > the appropriate convert() method but couldn't find it. > > (2) I ran @code_warntype on the above segment and found something > worrisome: the compiler apparently thinks that both k and v are of type > Union{Int,Float64}. Why can't it infer the correct types? Is there a > performance loss from the compiler's inability to know the correct types? > > The reason I ask is that I have developed SortedDict for the > DataStructures.jl package, and currently eltype{SortedDict{K,V}) is defined > to be Tuple{K,V} rather than Pair{K,V} so it is incompatible with Dict. > I'm trying to understand the relevant issues in order to fix this. I am > running Julia 0.4, 15-day-old master. > > Thanks, > Steve Vavasis > >
