Add hasproperty and hasfield to Base RFC

NEWS.md

@@ -29,6 +29,8 @@ New library functions
 Standard library changes
 ------------------------
 
+* Added `Base.hasproperty` and `Base.hasfield` ([#28850]).
+
 #### LinearAlgebra
 
 * Added keyword arguments `rtol`, `atol` to `pinv` and `nullspace` ([#29998]).

base/exports.jl

@@ -700,7 +700,9 @@ export
  fieldnames,
  fieldcount,
  fieldtypes,
+ hasfield,
  propertynames,
+ hasproperty,
  isabstracttype,
  isbitstype,
  isprimitivetype,

base/reflection.jl

@@ -176,6 +176,17 @@ fieldnames(::Core.TypeofBottom) =
  throw(ArgumentError("The empty type does not have field names since it does not have instances."))
 fieldnames(t::Type{<:Tuple}) = ntuple(identity, fieldcount(t))
 
+"""
+ hasfield(T::Type, name::Symbol)
+
+Returns a boolean indicating whether DataType has the specified field as one of
+its own fields.
+"""
+function hasfield(::Type{T}, name::Symbol) where T
+ @_pure_meta
+ return fieldindex(T, name, false) > 0
+end
+
 """
  nameof(t::DataType) -> Symbol
 
@@ -1204,3 +1215,11 @@ 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
+
+"""
+ hasproperty(x, s::Symbol)
+
+Returns a boolean indicating whether the object `x` has the specified property as one of
+its own properties.
+"""
+hasproperty(x, s::Symbol) = s in propertynames(x)

test/reflection.jl

@@ -221,6 +221,10 @@ mutable struct TLayout
 end
 tlayout = TLayout(5,7,11)
 @test fieldnames(TLayout) == (:x, :y, :z) == Base.propertynames(tlayout)
+@test hasfield(TLayout, :y)
+@test !hasfield(TLayout, :a)
+@test hasproperty(tlayout, :x)
+@test !hasproperty(tlayout, :p)
 @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 fieldnames(Complex) === (:re, :im)