# Fields with abstract types in Base and StdLib

**URL:** <https://discourse.julialang.org/t/fields-with-abstract-types-in-base-and-stdlib/12634>\
**Category:** Internals & Design\
**Created:** [July 24, 2018, 1:26pm UTC](https://discourse.julialang.org/t/fields-with-abstract-types-in-base-and-stdlib/12634 "2018-07-24T13:26:01Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Diego\_Javier\_Zea](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/diego_javier_zea/32/1858_2.png) [@Diego\_Javier\_Zea](https://discourse.julialang.org/u/Diego_Javier_Zea)\
**Post date:** [July 24, 2018, 1:26pm UTC](https://discourse.julialang.org/t/fields-with-abstract-types-in-base-and-stdlib/12634/1 "2018-07-24T13:26:01Z")

</div>

Hi!

`eachline` was slow because the `EachLine` `stream` field has the abstract type `IO` and it can be solved by [using a type parameter for `stream` in `EachLine`](https://github.com/JuliaLang/julia/pull/28253). So, I looked for other structures in Base and StdLib (Julia 0.7.0-beta2.81) with [abstract type fields](https://docs.julialang.org/en/latest/manual/performance-tips/#Avoid-fields-with-abstract-type-1) that could lead to hidden performance issues. Here are the bash lines I’ve used to find them and the list of the files that define `struct`s with abstract type fields (with small editions to make them more leggible or complete):

```julia
~/bin/julia-fdad5051ff/share/julia/base$ ag "^abstract type .* end" | cut -d" " -f3 | cut -d"{" -f1 > ~/abstract_types.txt 
~/bin/julia-fdad5051ff/share/julia/base$ for t in $(cat ~/abstract_types.txt); do ag -B 3 "^\s+[a-zA-Z0-9]+::$t\s*$"; done

logging.jl
359-struct LogState
360- min_enabled_level::LogLevel
361: logger::AbstractLogger

strings/string.jl
8-struct StringIndexError <: Exception
9- string::AbstractString
10: index::Integer

logging.jl
500-struct SimpleLogger <: AbstractLogger
501: stream::IO

multimedia.jl
201-struct TextDisplay <: AbstractDisplay
202: io::IO

process.jl
299-mutable struct Process <: AbstractPipe
300- cmd::Cmd
301- handle::Ptr{Cvoid}
302: in::IO
303: out::IO
304: err::IO

io.jl
845-struct EachLine
846: stream::IO

process.jl
74-struct OrCmds <: AbstractCmd
75: a::AbstractCmd
76: b::AbstractCmd
80-struct ErrOrCmds <: AbstractCmd
81: a::AbstractCmd
82: b::AbstractCmd
86-struct AndCmds <: AbstractCmd
87: a::AbstractCmd
88: b::AbstractCmd
157-struct CmdRedirect <: AbstractCmd
158: cmd::AbstractCmd

~/bin/julia-fdad5051ff/share/julia/base$ cd ../stdlib/v0.7/
~/bin/julia-fdad5051ff/share/julia/stdlib/v0.7$ ag "^abstract type .* end" | cut -d" " -f3 | cut -d"{" -f1 >> ~/abstract_types.txt 
~/bin/julia-fdad5051ff/share/julia/stdlib/v0.7$ for t in $(cat ~/abstract_types.txt); do ag -B 3 "^\s+[a-zA-Z0-9]+::$t\s*$"; done

LinearAlgebra/src/cholesky.jl
46-struct CholeskyPivoted{T,S<:AbstractMatrix} <: Factorization{T}
47- factors::S
48- uplo::Char
49- piv::Vector{BlasInt}
50- rank::BlasInt
51: tol::Real

Distributed/test/topology.jl
37-mutable struct TopoTestManager <: ClusterManager
38: np::Integer

Distributed/src/managers.jl
289-struct LocalManager <: ClusterManager
290: np::Integer

Logging/src/ConsoleLogger.jl
25-struct ConsoleLogger <: AbstractLogger
26: stream::IO

REPL/src/REPL.jl
1038-mutable struct StreamREPL <: AbstractREPL
1039: stream::IO

Base64/src/encode.jl
34-struct Base64EncodePipe <: IO
35: io::IO

Base64/src/decode.jl
35-struct Base64DecodePipe <: IO
36: io::IO

Distributed/src/process_messages.jl
5-mutable struct RemoteValue
6: c::AbstractChannel

REPL/src/REPLCompletions.jl
54-struct DictCompletion <: Completion
55: dict::AbstractDict

LinearAlgebra/src/cholesky.jl
46-struct CholeskyPivoted{T,S<:AbstractMatrix} <: Factorization{T}
47- factors::S
48- uplo::Char
49- piv::Vector{BlasInt}
50- rank::BlasInt
51: tol::Real

Distributed/src/cluster.jl
53-mutable struct Worker
54- id::Int
55- del_msgs::Array{Any,1}
56- add_msgs::Array{Any,1}
57- gcflag::Bool
58- state::WorkerState
59- c_state::Condition # wait for state changes
60- ct_time::Float64 # creation time
61- conn_func::Any # used to setup connections lazily
62-
63- r_stream::IO
64- w_stream::IO
65- w_serializer::ClusterSerializer # writes can happen from any task hence store the
66- # serializer as part of the Worker object
67: manager::ClusterManager

REPL/src/LineEdit.jl
69-mutable struct PromptState <: ModeState
70: terminal::AbstractTerminal
1542-mutable struct SearchState <: ModeState
1543: terminal::AbstractTerminal
1599-mutable struct PrefixSearchState <: ModeState
1600: terminal::AbstractTerminal

REPL/src/REPL.jl
199-mutable struct BasicREPL <: AbstractREPL
200: terminal::TextTerminal
304-mutable struct LineEditREPL <: AbstractREPL
305: t::TextTerminal

```

Maybe those `struct`s can use type parameters or use more specific types for their fields.

Cheers,