https://issues.dlang.org/show_bug.cgi?id=20424

          Issue ID: 20424
           Summary: A constructor with a value argument of the same type
                    as being constructed should be an error
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: bugzilla@digitalmars.com

extern(C) void puts(const char*);

  struct S {
    this(S)  // should be a compile time error
    { puts("works fine"); }
  }

  void main() {
    S a;
    S b = S(a);
  }

It should call itself recursively and crash. The fact that it appears to run successfully is also a bug. Copy constructors must take their first argument by reference.

https://github.com/dlang/DIPs/blob/master/DIPs/accepted/DIP1018.md

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