RFC: Base.propertynames(x), analogous to fieldnames(typeof(x))

NEWS.md

@@ -38,7 +38,8 @@ New language features
     and implements three-valued logic, similar to SQLs `NULL` and R's `NA`.
 
   * Field access via dot-syntax can now be overloaded by adding methods to
-    `Base.getproperty` and `Base.setproperty!` ([#1974]).
+    `Base.getproperty` and `Base.setproperty!` ([#1974]), optionally along with
+    a corresponding `Base.propertynames` method for reflection ([#25311]).
 
   * Values for `Enum`s can now be specified inside of a `begin` block when using the
     `@enum` macro ([#25424]).

base/exports.jl

@@ -865,6 +865,7 @@ export
     fieldname,
     fieldnames,
     fieldcount,
+    # propertynames,
     isconcrete,
     oftype,
     promote,

base/linalg/bunchkaufman.jl

@@ -205,6 +205,8 @@ function getproperty(B::BunchKaufman{T}, d::Symbol) where {T<:BlasFloat}
     end
 end
 
+Base.propertynames(B::BunchKaufman, private::Bool=false) = append!([:p,:P,:L,:U,:D], private ? fieldnames(typeof(B)) : Symbol[])
+
 issuccess(B::BunchKaufman) = B.info == 0
 
 function Base.show(io::IO, mime::MIME{Symbol("text/plain")}, B::BunchKaufman)

base/linalg/cholesky.jl

@@ -393,6 +393,8 @@ function getproperty(C::Cholesky, d::Symbol)
         return getfield(C, d)
     end
 end
+Base.propertynames(F::Cholesky, private::Bool=false) = append!([:U,:L,:UL], private ? fieldnames(typeof(F)) : Symbol[])
+
 function getproperty(C::CholeskyPivoted{T}, d::Symbol) where T<:BlasFloat
     Cfactors = getfield(C, :factors)
     Cuplo    = getfield(C, :uplo)
@@ -413,6 +415,7 @@ function getproperty(C::CholeskyPivoted{T}, d::Symbol) where T<:BlasFloat
         return getfield(C, d)
     end
 end
+Base.propertynames(F::CholeskyPivoted, private::Bool=false) = append!([:U,:L,:p,:P], private ? fieldnames(typeof(F)) : Symbol[])
 
 issuccess(C::Cholesky) = C.info == 0
 

base/linalg/hessenberg.jl

@@ -66,6 +66,8 @@ function getproperty(F::Hessenberg, d::Symbol)
     return getfield(F, d)
 end
 
+Base.propertynames(F::Hessenberg, private::Bool=false) = append!([:Q,:H], private ? fieldnames(typeof(F)) : Symbol[])
+
 function getindex(A::HessenbergQ, i::Integer, j::Integer)
     x = zeros(eltype(A), size(A, 1))
     x[i] = 1

base/linalg/lq.jl

@@ -85,6 +85,8 @@ function getproperty(F::LQ, d::Symbol)
     end
 end
 
+Base.propertynames(F::LQ, private::Bool=false) = append!([:L,:Q], private ? fieldnames(typeof(F)) : Symbol[])
+
 getindex(A::LQPackedQ, i::Integer, j::Integer) =
     mul!(A, setindex!(zeros(eltype(A), size(A, 2)), 1, j))[i]
 

base/linalg/lu.jl

@@ -268,6 +268,8 @@ function getproperty(F::LU{T,<:StridedMatrix}, d::Symbol) where T
     end
 end
 
+Base.propertynames(F::LU, private::Bool=false) = append!([:L,:U,:p,:P], private ? fieldnames(typeof(F)) : Symbol[])
+
 issuccess(F::LU) = F.info == 0
 
 function show(io::IO, mime::MIME{Symbol("text/plain")}, F::LU)

base/linalg/qr.jl

@@ -449,6 +449,7 @@ function getproperty(F::QRCompactWY, d::Symbol)
         getfield(F, d)
     end
 end
+Base.propertynames(F::Union{QR,QRCompactWY}, private::Bool=false) = append!([:R,:Q], private ? fieldnames(typeof(F)) : Symbol[])
 function getproperty(F::QRPivoted{T}, d::Symbol) where T
     m, n = size(F)
     if d == :R
@@ -469,6 +470,7 @@ function getproperty(F::QRPivoted{T}, d::Symbol) where T
         getfield(F, d)
     end
 end
+Base.propertynames(F::QRPivoted, private::Bool=false) = append!([:R,:Q,:p,:P], private ? fieldnames(typeof(F)) : Symbol[])
 
 abstract type AbstractQ{T} <: AbstractMatrix{T} end
 

base/linalg/schur.jl

@@ -77,6 +77,8 @@ function getproperty(F::Schur, d::Symbol)
     end
 end
 
+Base.propertynames(F::Schur) = append!([:Schur,:vectors], fieldnames(typeof(F)))
+
 function show(io::IO, F::Schur)
     println(io, "$(typeof(F)) with factors T and Z:")
     show(io, F.T)
@@ -274,6 +276,8 @@ function getproperty(F::GeneralizedSchur, d::Symbol)
     end
 end
 
+Base.propertynames(F::GeneralizedSchur) = append!([:values,:left,:right], fieldnames(typeof(F)))
+
 """
     schur(A::StridedMatrix, B::StridedMatrix) -> S::StridedMatrix, T::StridedMatrix, Q::StridedMatrix, Z::StridedMatrix, α::Vector, β::Vector
 

base/linalg/svd.jl

@@ -186,6 +186,8 @@ function getproperty(F::SVD, d::Symbol)
     end
 end
 
+Base.propertynames(F::SVD, private::Bool=false) = private ? append!([:V], fieldnames(typeof(F))) : [:U,:S,:V,:Vt]
+
 """
     svdvals!(A)
 
@@ -461,6 +463,8 @@ svd(x::Number, y::Number) = first.(svd(fill(x, 1, 1), fill(y, 1, 1)))
     end
 end
 
+Base.propertynames(F::GeneralizedSVD) = append!([:alpha,:beta,:vals,:S,:D1,:D2,:R0], fieldnames(typeof(F)))
+
 """
     svdvals!(A, B)
 

base/reflection.jl

@@ -1119,3 +1119,20 @@ min_world(m::Method) = reinterpret(UInt, m.min_world)
 max_world(m::Method) = typemax(UInt)
 min_world(m::Core.MethodInstance) = reinterpret(UInt, m.min_world)
 max_world(m::Core.MethodInstance) = reinterpret(UInt, m.max_world)
+
+"""
+    propertynames(x, private=false)
+
+Get an array of the properties (`x.property`) of an object `x`.   This
+is typically the same as [`fieldnames(typeof(x))`](@ref), but types
+that overload [`getproperty`](@ref) should generally overload `propertynames`
+as well to get the properties of an instance of the type.
+
+`propertynames(x)` may return only "public" property names that are part
+of the documented interface of `x`.   If you want it to also return "private"
+fieldnames intended for internal use, pass `true` for the optional second argument.
+REPL tab completion on `x.` shows only the `private=false` properties.
+"""
+propertynames(x) = fieldnames(typeof(x))
+propertynames(m::Module) = names(m)
+propertynames(x, private) = propertynames(x) # ignore private flag by default

base/repl/REPLCompletions.jl

@@ -5,6 +5,7 @@ module REPLCompletions
 export completions, shell_completions, bslash_completions
 
 using Base.Meta
+using Base: propertynames
 
 function completes_global(x, name)
     return startswith(x, name) && !('#' in x)
@@ -40,6 +41,7 @@ function complete_symbol(sym, ffunc)
 
     lookup_module = true
     t = Union{}
+    val = nothing
     if findlast(occursin(non_identifier_chars), sym) < findlast(equalto('.'), sym)
         # Find module
         lookup_name, name = rsplit(sym, ".", limit=2)
@@ -48,6 +50,7 @@ function complete_symbol(sym, ffunc)
 
         b, found = get_value(ex, context_module)
         if found
+            val = b
             if isa(b, Module)
                 mod = b
                 lookup_module = true
@@ -81,6 +84,13 @@ function complete_symbol(sym, ffunc)
         else
             append!(suggestions, filtered_mod_names(p, mod, name, true, false))
         end
+    elseif val !== nothing # looking for a property of an instance
+        for property in propertynames(val, false)
+            s = string(property)
+            if startswith(s, name)
+                push!(suggestions, s)
+            end
+        end
     else
         # Looking for a member of a type
         if t isa DataType && t != Any

doc/src/base/base.md

@@ -319,6 +319,7 @@ Core.nfields
 Base.fieldnames
 Base.fieldname
 Base.fieldcount
+Base.propertynames
 Base.datatype_module
 Base.datatype_name
 Base.isconst

test/linalg/lu.jl

@@ -264,3 +264,10 @@ U factor:
  0.0  0.0  1.0  0.0
  0.0  0.0  0.0  1.0"""
 end
+
+@testset "propertynames" begin
+    names = sort!(string.(Base.propertynames(lufact(rand(3,3)))))
+    @test names == ["L", "P", "U", "p"]
+    allnames = sort!(string.(Base.propertynames(lufact(rand(3,3)), true)))
+    @test allnames == ["L", "P", "U", "factors", "info", "ipiv", "p"]
+end

test/reflection.jl

@@ -333,7 +333,7 @@ mutable struct TLayout
     z::Int32
 end
 tlayout = TLayout(5,7,11)
-@test fieldnames(TLayout) == [:x, :y, :z]
+@test fieldnames(TLayout) == [:x, :y, :z] == Base.propertynames(tlayout)
 @test [(fieldoffset(TLayout,i), fieldname(TLayout,i), fieldtype(TLayout,i)) for i = 1:fieldcount(TLayout)] ==
     [(0, :x, Int8), (2, :y, Int16), (4, :z, Int32)]
 @test_throws BoundsError fieldtype(TLayout, 0)