Add nameof dispatches on operators

This previously relied on `Operator <: Function` and `Function` just happens to have `nameof` defined.

Author: ChrisRackauckas

Project.toml

@@ -109,7 +109,7 @@ SpecialFunctions = "0.7, 0.8, 0.9, 0.10, 1.0, 2"
 StaticArrays = "0.10, 0.11, 0.12, 1.0"
 SymbolicIndexingInterface = "0.3.12"
 SymbolicUtils = "2.1"
-Symbolics = "5.30.1"
+Symbolics = "5.32"
 URIs = "1"
 UnPack = "0.1, 1.0"
 Unitful = "1.1"

src/discretedomain.jl

@@ -4,6 +4,7 @@ struct SampleTime <: Operator
     SampleTime() = SymbolicUtils.term(SampleTime, type = Real)
 end
 SymbolicUtils.promote_symtype(::Type{<:SampleTime}, t...) = Real
+Base.nameof(::SampleTime) = :SampleTime
 
 # Shift
 
@@ -32,6 +33,8 @@ struct Shift <: Operator
 end
 Shift(steps::Int) = new(nothing, steps)
 normalize_to_differential(s::Shift) = Differential(s.t)^s.steps
+Base.nameof(::Shift) = :Shift
+
 function (D::Shift)(x, allow_zero = false)
     !allow_zero && D.steps == 0 && return x
     Term{symtype(x)}(D, Any[x])
@@ -108,6 +111,7 @@ Sample(x) = Sample()(x)
 (D::Sample)(x) = Term{symtype(x)}(D, Any[x])
 (D::Sample)(x::Num) = Num(D(value(x)))
 SymbolicUtils.promote_symtype(::Sample, x) = x
+Base.nameof(::Sample) = :Sample
 
 Base.show(io::IO, D::Sample) = print(io, "Sample(", D.clock, ")")
 
@@ -137,6 +141,7 @@ end
 (D::Hold)(x) = Term{symtype(x)}(D, Any[x])
 (D::Hold)(x::Num) = Num(D(value(x)))
 SymbolicUtils.promote_symtype(::Hold, x) = x
+Base.nameof(::Hold) = :Hold
 
 Hold(x) = Hold()(x)