import std.stdio;

​

@safe:

​

struct ScopeBuffer

{

    this(char[4] buf, size_t len = 0)

    {

        this.buf = buf;

        this.len = len;

    }

    char[] opSlice(size_t lower, size_t upper)

    in

    {

        assert(lower <= len, "Lower bound must be less than or equal to the length");

        assert(upper <= len, "Upper bound must be less than or equal to the length");

        assert(lower <= upper, "Lower bound must be less than or equal to the upper bound");

    }

    do

    {

        return buf[lower .. upper]; // GOOD: Compiler error here

    }

    char[4] buf;

    size_t len;

}

​

char[] fun()

{

    char[4] buf = "abcd";

    auto sb = ScopeBuffer(buf, 4);

    return sb[0..2];

}

​

void main()

{

    auto s = fun();

    writeln(s);

}