Using MathOptInterface.AbstractOptimizer in parametric type declaration

Specific Domains Optimization (Mathematical)
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2

The issue is that TestType(Ipopt.Optimizer) is passing in the type of an optimizer, not an instance of it.

You either need TestType(Ipopt.Optimizer()), or you need something like:

julia> struct TestType{U<:Real}
           test::Type{U}
       end

julia> TestType(Int)
TestType{Int64}(Int64)

julia> TestType(1)
ERROR: MethodError: no method matching TestType(::Int64)

Closest candidates are:
  TestType(::Type{U}) where U<:Real
   @ Main REPL[1]:2

Stacktrace:
 [1] top-level scope
   @ REPL[3]:1

It might help your understanding to try examples with Real instead of MOI.AbstractOptimizer:

julia> struct TestType{U<:Real}
           test::U
       end

julia> TestType(Int)
ERROR: MethodError: no method matching TestType(::Type{Int64})

Closest candidates are:
  TestType(::U) where U<:Real
   @ Main REPL[1]:2

Stacktrace:
 [1] top-level scope
   @ REPL[2]:1

julia> TestType(1)
TestType{Int64}(1)

However, from a JuMP perspective, you probably just want to make this:

struct TestType
    test::Any
end

This would support

GRB_ENV = Gurobi.Env()
TestType(() -> Gurobi.Optimizer(GRB_ENV))

and

TestType(optimizer_with_attributes(Ipopt.Optimizer, "tol" => 1e-8))

JuMP’s optimizer constructors do to need to be <:MOI.AbstractOptimizer.

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