set_element_type_not_assignable    
                  The element type '{0}' can't be assigned to the set type '{1}'.
Description
#The analyzer produces this diagnostic when an element in a set literal has a type that isn't assignable to the element type of the set.
Example
#
                    The following code produces this diagnostic because the type of the string
                    literal '0' is String, which isn't assignable to int, the element
                    type of the set:
                  
                      dart
                      
                  var s = <int>{'0'};
Common fixes
#If the element type of the set literal is wrong, then change the element type of the set:
                      dart
                      
                  var s = <String>{'0'};
If the type of the element is wrong, then change the element:
                      dart
                      
                  var s = <int>{'0'.length};