fix hash for Operation

Author: shashi

src/operations.jl

@@ -54,6 +54,8 @@ Base.isequal(::Variable , ::Operation) = false
 Base.isequal(::Operation, ::Constant ) = false
 Base.isequal(::Constant , ::Operation) = false
 
+Base.hash(o::Operation, salt::UInt) = hash(o.args, hash(o.op, salt))
+
 # provide iszero for Operations to help sparse addition and multiplication
 # e.g., we want to tell the sparse library that iszero(zero(Operation) + zero(Operation)) == true
 Base.iszero(x::Operation) = (_x = simplify(x); _x isa Constant && iszero(_x.value))

test/operation_overloads.jl

@@ -5,6 +5,16 @@ using Test
 
 @variables a,b,c,d
 
+# test hashing
+aa = a; # old a
+
+@variables a
+
+@test isequal(a, aa)
+@test hash(a) == hash(aa)
+
+@test isequal(get_variables(a+aa+1), [a])
+
 # test some matrix operations don't throw errors
 X = [a b;c d]
 det(X)