fix(vertex): use varying string to allow elemental functions

Author: everythingfunctional

src/dag_s.f90

@@ -215,8 +215,8 @@ pure function generate_digraph(self) result(str)
 
       ! define the vertices:
       do i=1,size(self%vertices)
-        label = 'label="'//trim(adjustl(self%vertices(i)%label()))//'"'
-        attributes = '['//trim(adjustl(self%vertices(i)%attributes()))//','//label//']'
+        label = char('label="'//self%vertices(i)%label()//'"')
+        attributes = char('['//self%vertices(i)%attributes()//','//label//']')
         str = str//tab//integer_to_string(i)//' '//attributes//newline
         if (i==size(self%vertices)) str = str//newline
       end do

src/vertex_m.f90

@@ -5,7 +5,7 @@ module vertex_m
   !! date: 2020-Nov-30
   !! license: Copyright (c) 2020-2021, Sourcery Institute, BSD 3-clause license Copyright (c) 2018 Jacob Williams
     use jsonff, only : json_element_t, json_object_t, json_value_t
-    use iso_varying_string, only : varying_string, len
+    use iso_varying_string, only : varying_string
 
     implicit none
 
@@ -17,7 +17,7 @@ module vertex_m
       private
       integer, allocatable :: edges_(:)
       type(varying_string) :: label_
-      character(len=:), allocatable :: attributes_
+      type(varying_string) :: attributes_
     contains
       procedure :: to_json
       procedure :: edges
@@ -87,14 +87,14 @@ elemental module function label(self) result(my_label)
         !! Vertex label getter
         implicit none
         class(vertex_t), intent(in) :: self
-        character(len=len(self%label_)) my_label
+        type(varying_string) my_label
       end function
 
       elemental module function attributes(self) result(my_attributes)
         !! Vertex attributes getter
         implicit none
         class(vertex_t), intent(in) :: self
-        character(len=len(self%attributes_)) my_attributes
+        type(varying_string) my_attributes
       end function
 
     end interface

src/vertex_s.f90

@@ -61,7 +61,7 @@
     vertex%edges_ = edges
     vertex%label_ = label
     if (present(attributes)) then
-      vertex%attributes_ = char(attributes)
+      vertex%attributes_ = attributes
     else
       vertex%attributes_ = branch
     end if