How to specify the type of the read result?

[zhaoli-IHEP]

Hello. We are trying to read a JLD file directly. However, the @code_warntype gives warning that the returned result of read() is ::Any, and consequently the length of the string is also ::Any. So we guess the problem is how to specify the type of the read result. Is there anyway?

function test_JLD()

  file = jldopen( "test.jld", "r" )
  for index in 1:4
    test_str = read( file, "test$index" )
    len = length(test_str)
    if len > 125
      println( "too long" )
    end # if
  end # for index
  close(file)

  return nothing
end # function test_JLD

@code_warntype test_JLD()

And here is the message from @code_warntype

Variables
  #self#::Core.Compiler.Const(test_JLD, false)
  file::Union{JLD.JldFile, JLD.JLD00.JldFile}
  @_3::Union{Nothing, Tuple{Int64,Int64}}
  index::Int64
  test_str::Any
  len::Any

Body::Nothing
1 ─       (file = Main.jldopen("test.jld", "r"))
│   %2  = (1:4)::Core.Compiler.Const(1:4, false)
│         (@_3 = Base.iterate(%2))
│   %4  = (@_3::Core.Compiler.Const((1, 1), false) === nothing)::Core.Compiler.Const(false, false)
│   %5  = Base.not_int(%4)::Core.Compiler.Const(true, false)
└──       goto #6 if not %5
2 ┄ %7  = @_3::Tuple{Int64,Int64}::Tuple{Int64,Int64}
│         (index = Core.getfield(%7, 1))
│   %9  = Core.getfield(%7, 2)::Int64
│   %10 = file::Union{JLD.JldFile, JLD.JLD00.JldFile}
│   %11 = Base.string("test", index)::String
│         (test_str = Main.read(%10, %11))
│         (len = Main.length(test_str))
│   %14 = (len > 125)::Any
└──       goto #4 if not %14
3 ─       Main.println("too long")
4 ┄       (@_3 = Base.iterate(%2, %9))
│   %18 = (@_3 === nothing)::Bool
│   %19 = Base.not_int(%18)::Bool
└──       goto #6 if not %19
5 ─       goto #2
6 ┄       Main.close(file)
└──       return Main.nothing

As you can see the test_str::Any and len::Any are warned. Also the file variable, which is in the for loop, is warned file::Union{JLD.JldFile, JLD.JLD00.JldFile}.