https://issues.dlang.org/show_bug.cgi?id=14246

          Issue ID: 14246
           Summary: proper destruction of partially constructed
                    objects/structs
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: DMD
          Assignee: nobody@puremagic.com
          Reporter: schuetzm@gmx.net

Currently, when a constructor throws, it will not call destructors of already initialized member fields. The user is responsible for catching exceptions or using `scope(failure)` and cleaning up manually. Of course, this is error prone and can easily be forgotten.

I suggest to apply the same heuristic to mutable fields that is also use for tracking the initialization of immutable fields: The first "assignment" to a field must not appear in a loop or after a label, and calls the constructor instead of opAssign(). For immutable and const fields, no further writes are allowed; mutable fields can be changed as desired.

At each point where an exception can occur, the compiler is then aware which fields have already been initialized, and can call their destructor.

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