From 5dfdbc84903d55d75e6a2a6d0fb99ef1f20d4a4a Mon Sep 17 00:00:00 2001
From: Martin Holters <martin.holters@hsu-hh.de>
Date: Mon, 16 Jan 2023 13:59:51 +0100
Subject: [PATCH 1/2] Avoid using element equality for finding elements in
 circuit

Note the following change:

Before:
```julia
julia> R = resistor(1000); circ = Circuit();

julia> add!(circ, R)
Symbol("##296")

julia> add!(circ, R)
Symbol("##296")

julia> ACME.nb(circ)
1
```
After:
```julia
julia> R = resistor(1000); circ = Circuit();

julia> add!(circ, R)
Symbol("##296")

julia> add!(circ, R)
Symbol("##297")

julia> ACME.nb(circ)
2
```
I.e. the same element can now be added twice. In general, element
instances should not have an identity, so the new behaviour seems more
reasonable. (The same `R` could already be added to another circuit
without having any effect on its presence in the first one, for
example.)
---
 src/circuit.jl | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/src/circuit.jl b/src/circuit.jl
index 3b36dcf4..1adc64df 100644
--- a/src/circuit.jl
+++ b/src/circuit.jl
@@ -1,4 +1,4 @@
-# Copyright 2015, 2016, 2017, 2018, 2019, 2020, 2021 Martin Holters
+# Copyright 2015, 2016, 2017, 2018, 2019, 2020, 2021, 2023 Martin Holters
 # See accompanying license file.
 
 export Circuit, add!, connect!, disconnect!, @circuit, composite_element
@@ -53,9 +53,8 @@ function incidence(c::Circuit)
     j = sizehint!(Int[], 2nb(c))
     v = sizehint!(Int[], 2nb(c))
     for (row, pins) in enumerate(c.nets), (elemname, pinname) in pins
-        elem = c.elements[elemname]
-        offset = branch_offset(c, elem)
-        bps = elem.pins[pinname]
+        offset = branch_offset(c, elemname)
+        bps = c.elements[elemname].pins[pinname]
         for (branch, polarity) in bps
             push!(i, row)
             push!(j, offset + branch)
@@ -93,11 +92,6 @@ Adds the element `elem` to the circuit `c`, creating and returning a new, unique
 reference designator, leaving its pins unconnected.
 """
 function add!(c::Circuit, elem::Element)
-    for (k, v) in c.elements
-        if v == elem
-            return k
-        end
-    end
     designator = gensym()
     add!(c, designator, elem)
     return designator
@@ -135,10 +129,10 @@ function Base.delete!(c::Circuit, designator::Symbol)
     delete!(c.elements, designator)
 end
 
-function branch_offset(c::Circuit, elem::Element)
+function branch_offset(c::Circuit, designator::Symbol)
     offset = 0
-    for el in elements(c)
-        el == elem && return offset
+    for (des, el) in c.elements
+        des === designator && return offset
         offset += nb(el)
     end
     throw(ArgumentError("Element not found in circuit"))

From 8f992d13e6b1fd0fc4aafe1900f99137acc73205 Mon Sep 17 00:00:00 2001
From: Martin Holters <martin.holters@hsu-hh.de>
Date: Tue, 17 Jan 2023 07:14:50 +0100
Subject: [PATCH 2/2] Implement `==` (and `hash`) for `Element`

So that e.g. `resistor(1000) == resistor(1000)`, which previously gave
`false`.
---
 src/ACME.jl      |  7 ++++++-
 test/runtests.jl | 12 +++++++++++-
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/src/ACME.jl b/src/ACME.jl
index ffbec765..d78270d5 100644
--- a/src/ACME.jl
+++ b/src/ACME.jl
@@ -1,4 +1,4 @@
-# Copyright 2015, 2016, 2017, 2018, 2019, 2020, 2021 Martin Holters
+# Copyright 2015, 2016, 2017, 2018, 2019, 2020, 2021, 2023 Martin Holters
 # See accompanying license file.
 
 module ACME
@@ -97,6 +97,11 @@ struct Element
     end
 end
 
+Base.:(==)(e1::Element, e2::Element) =
+    all(f -> (getfield(e1, f) == getfield(e2, f))::Bool, fieldnames(Element))
+Base.hash(e::Element, h::UInt) =
+    foldl((h, f) -> hash(getfield(e, f), h)::UInt, fieldnames(Element); init=h)
+
 for (n,m) in Dict(:nb => :mv, :nx => :mx, :nq => :mq, :nu => :mu)
   @eval ($n)(e::Element) = size(e.$m, 2)
 end
diff --git a/test/runtests.jl b/test/runtests.jl
index 169f1447..6f33609f 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1,4 +1,4 @@
-# Copyright 2015, 2016, 2017, 2018, 2019, 2020, 2021, 2022 Martin Holters
+# Copyright 2015, 2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023 Martin Holters
 # See accompanying license file.
 
 include("checklic.jl")
@@ -40,6 +40,16 @@ end
     @test !ACME.setlhs!(solver, zeros(3,3))
 end
 
+@testset "Element equality" begin
+    @test resistor(1e3) == resistor(1e3)
+    @test hash(resistor(1e3)) == hash(resistor(1e3))
+    @test resistor(1e3) != resistor(2.2e3)
+    @test resistor(1) != voltagesource(1)
+    @test bjt(:npn) == bjt(:npn)
+    @test hash(bjt(:npn)) == hash(bjt(:npn))
+    @test bjt(:npn) != bjt(:pnp)
+end
+
 @testset "simple circuits" begin
     @testset "empty circuit" begin
         circ = @circuit begin end