Allow creating model from parts

Author: blegat

src/Utilities/matrix_of_constraints.jl

@@ -92,13 +92,24 @@ mutable struct MatrixOfConstraints{T,AT,BT,ST} <: MOI.ModelLike
     caches::Vector{Any}
     are_indices_mapped::Vector{BitSet}
     final_touch::Bool
-    function MatrixOfConstraints{T,AT,BT,ST}() where {T,AT,BT,ST}
-        model = new{T,AT,BT,ST}(AT(), BT(), ST(), Any[], BitSet[], false)
+    function MatrixOfConstraints{T}(coefficients, constants, sets) where {T}
+        model = new{T,typeof(coefficients),typeof(constants),typeof(sets)}(
+            coefficients,
+            constants,
+            sets,
+            Any[],
+            BitSet[],
+            false,
+        )
         MOI.empty!(model)
         return model
     end
 end
 
+function MatrixOfConstraints{T,AT,BT,ST}() where {T,AT,BT,ST}
+    return MatrixOfConstraints{T}(AT(), BT(), ST())
+end
+
 ###
 ### Interface for the .coefficients field
 ###

src/Utilities/model.jl

@@ -32,12 +32,12 @@ mutable struct GenericModel{T,O,V,C} <: AbstractModelLike{T}
     # A useful dictionary for extensions to store things. These are
     # _not_ copied between models.
     ext::Dict{Symbol,Any}
-    function GenericModel{T,O,V,C}() where {T,O,V,C}
-        return new{T,O,V,C}(
+    function GenericModel{T}(objective, variables, constraints) where {T}
+        return new{T,typeof(objective),typeof(variables),typeof(constraints)}(
             "",
-            O(),
-            V(),
-            C(),
+            objective,
+            variables,
+            constraints,
             Dict{MOI.VariableIndex,String}(),
             nothing,
             Dict{MOI.ConstraintIndex,String}(),
@@ -47,6 +47,10 @@ mutable struct GenericModel{T,O,V,C} <: AbstractModelLike{T}
     end
 end
 
+function GenericModel{T,O,V,C}() where {T,O,V,C}
+    return GenericModel{T}(O(), V(), C())
+end
+
 abstract type AbstractOptimizer{T} <: MOI.AbstractOptimizer end
 
 """