[Issue 1472] New: Be more clever about detecting assigment to non-l-values

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=1472

           Summary: Be more clever about detecting assigment to non-l-values
           Product: D
           Version: 1.020
          Platform: PC
        OS/Version: Windows
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla at digitalmars.com
        ReportedBy: wbaxter at gmail.com


It should be an error if you return a struct and then immediately just set one
of its fields in some way.

For instance
  struct Struct {
     int i;
     set_i(int _i) { i=_i; }
  }
  class Foo {
     Struct get_struct() { return s; }
     Struct s;
  } 

  Struct s;
  Foo x = new Foo;
  x.get_struct() = s;  // currently an error -- good
  x.get_struct.i = 10;  // currently not an error -- bad
  x.get_struct.set_i(10); // also current not an error -- bad


These errors are especially helpful in finding bugs when porting C++ code that
returned mutable references initially.  If you convert those to be
value-returning functions then you need to find all the places in the code that
are assuming the return value is an l-value.


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