`size` has no method matching size(::Data{Float32}) when using nested composite type in julia

Question

say I defined a composite type "Data" as follows:

type DataFormat
    format1::DataType
    format2::Uint
    format3::Uint
    format4::Ptr{None}
end

type Data{T} <: AbstractVector{T}
    value::Vector{T}
    format::DataFormat    
end

It's OK when I run myformat = DataFormat(Float32, 0, 0, C_NULL). But as I run this mydata = Data{Float32}([0.1, 0.2, 0.3], myformat), these errors appear:

Error showing value of type Data{Float32}:
ERROR: `size` has no method matching size(::Data{Float32})
in writemime at replutil.jl:18
in display at REPL.jl:117
in display at REPL.jl:120
in display at multimedia.jl:149
in print_response at REPL.jl:139
in print_response at REPL.jl:124
in anonymous at REPL.jl:586
in run_interface at /opt/homebrew-cask/Caskroom/julia/0.3.7/Julia-      0.3.7.app/Contents/Resources/julia/lib/julia/sys.dylib
in run_frontend at /opt/homebrew-cask/Caskroom/julia/0.3.7/Julia-0.3.7.app/Contents/Resources/julia/lib/julia/sys.dylib
in run_repl at /opt/homebrew-cask/Caskroom/julia/0.3.7/Julia-0.3.7.app/Contents/Resources/julia/lib/julia/sys.dylib
in _start at /opt/homebrew-cask/Caskroom/julia/0.3.7/Julia-0.3.7.app/Contents/Resources/julia/lib/julia/sys.dylib

It seems something broken with julia's size() function, how can I fix it? I'm very new to julia and don't know whether it's a good choice to use "nested" composite type like this?

ptb ptb · Accepted Answer · 2015-04-14T16:17:14

It's relatively straightforward to extend size:

julia> import Base.size

julia> size(d::Data) = size(d.value)
size (generic function with 51 methods)

If you want your datatype to support other operations like iteration and indexing you'll need to also define getindex, ~~start, next, length and done~~

Edit: See comment below for why start, next, length and done are not necessary.

`size` has no method matching size(::Data{Float32}) when using nested composite type in julia

1 Answers