[Issue 23557] New: Array concatenation ignores copy constructor

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23557

          Issue ID: 23557
           Summary: Array concatenation ignores copy constructor
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: druntime
          Assignee: nobody at puremagic.com
          Reporter: snarwin+bugzilla at gmail.com

As of DMD 2.101.0, the following program compiles and runs successfully to
completion:

---
struct S
{
    this(ref S)
    {
        assert(0);
    }
}

void main()
{
    S[] a = [ S() ];
    S[] b = a ~ a;
}
---

This program should assert at runtime when evaluating the expression `a ~ a`,
but does not, because the copy constructors of a's elements are not called.

If the copy constructor is changed to a postblit (`this(this)`), the program
asserts at runtime, as expected.

See also issue 23556, which affects appending to an array (~=), and issue
20879, which affected .dup and .idup.

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