Add write_to_file and read_from_file

src/copy.jl

@@ -144,3 +144,12 @@ end
 function Base.deepcopy(::Model)
     error("`JuMP.Model` does not support `deepcopy` as the reference to the underlying solver cannot be deep copied, use `copy` instead.")
 end
+
+function MOI.copy_to(dest::MOI.ModelLike, src::Model)
+    bridged_dest = MOI.Bridges.full_bridge_optimizer(dest, Float64)
+    return MOI.copy_to(bridged_dest, backend(src))
+end
+
+function MOI.copy_to(dest::Model, src::MOI.ModelLike)
+    return MOI.copy_to(backend(dest), src)
+end

src/file_formats.jl

@@ -21,8 +21,7 @@ function write_to_file(
     format::MathOptFormat.FileFormat = MathOptFormat.FORMAT_AUTOMATIC
 )
     dest = MathOptFormat.Model(format = format, filename = filename)
-    bridged_dest = MOI.Bridges.full_bridge_optimizer(dest, Float64)
-    MOI.copy_to(bridged_dest, backend(model))
+    MOI.copy_to(dest, model)
     MOI.write_to_file(dest, filename)
     return
 end
@@ -45,8 +44,7 @@ function Base.write(
         error("Unable to infer the file format from an IO stream.")
     end
     dest = MathOptFormat.Model(format = format)
-    bridged_dest = MOI.Bridges.full_bridge_optimizer(dest, Float64)
-    MOI.copy_to(bridged_dest, backend(model))
+    MOI.copy_to(dest, model)
     write(io, dest)
     return
 end
@@ -69,22 +67,22 @@ function read_from_file(
     src = MathOptFormat.Model(format = format, filename = filename)
     MOI.read_from_file(src, filename)
     model = Model()
-    MOI.copy_to(backend(model), src)
+    MOI.copy_to(model, src)
     return model
 end
 
 """
-    Base.read(io::IO, ::Type{Model}; format::FileFormat)
+    Base.read(io::IO, ::Type{Model}; format::MathOptFormat.FileFormat)
 
 Return a JuMP model read from `io` in the format `format`.
 """
-function Base.read(io::IO, ::Type{Model}; format::FileFormat)
+function Base.read(io::IO, ::Type{Model}; format::MathOptFormat.FileFormat)
     if format == MathOptFormat.FORMAT_AUTOMATIC
         error("Unable to infer the file format from an IO stream.")
     end
     src = MathOptFormat.Model(format = format)
     read!(io, src)
     model = Model()
-    MOI.copy_to(backend(model), src)
+    MOI.copy_to(model, src)
     return model
 end

test/file_formats.jl

@@ -37,7 +37,7 @@ using Test
         @test read("my_model.lp", String) ==
             "minimize\nobj: 2 x\nsubject to\nmy_c: 3 x >= 1\nBounds\nx >= 0\nEnd\n"
         @test_throws(
-            ErrorException("Read from file is not implemented for LP files."),
+            ErrorException("read! is not implemented for LP files."),
             read_from_file("my_model.lp")
         )
         rm("my_model.lp")