tensorcontract type stability

[khanley6]

Hi there,

It seems that tensorcontract, with its current definition, is type unstable:

julia> @code_warntype tensorcontract(A, a_idx, B, b_idx)
Variables
  #self#::Core.Compiler.Const(TensorOperations.tensorcontract, false)
  A::Array{Int64,2}
  IA::Tuple{Int64,Int64}
  B::Array{Int64,2}
  IB::Tuple{Int64,Int64}

Body::Array
1 ─ %1 = TensorOperations.symdiff(IA, IB)::Array{Int64,1}
│   %2 = (#self#)(A, IA, B, IB, %1)::Array
└──      return %2

However, changing the definition (tested below) results in stability:

julia> mytensorcontract(A, IA, B, IB, IC = Tuple(symdiff(IA, IB))) =
          tensorcontract(A, tuple(IA...), B, tuple(IB...), IC)
julia> @code_warntype mytensorcontract(A, a_idx, B, b_idx)
Variables
  #self#::Core.Compiler.Const(mytensorcontract, false)
  A::Array{Int64,2}
  IA::Tuple{Int64,Int64}
  B::Array{Int64,2}
  IB::Tuple{Int64,Int64}

Body::Union{}
1 ─ %1 = Main.symdiff(IA, IB)::Array{Int64,1}
│   %2 = Main.tuple(%1)::Tuple{Array{Int64,1}}
│        (#self#)(A, IA, B, IB, %2)
└──      Core.Compiler.Const(:(return %3), false)

I have made the change locally and all tests pass.

Is there any reason to use the current definition over the proposed one? I guess there is still an issue with passing an array explicitly:

c_idx::Array{Int} = ...
@code_warntype mytensorcontract(A, a_idx, B, b_idx, c_idx) #-> not stable
@code_warntype mytensorcontract(A, a_idx, B, b_idx, Tuple(c_idx)) #-> stable