import std.stdio;

​

@safe:

​

struct ScopeBuffer(T, size_t Len)

{

    this(T[Len] buf, size_t len = 0)

    {

        this.buf = buf;

        this.len = len;

    }

    // Decorateing `opSlice` with `return`, causes the compiler to correctly emit

    // a compiler error on line 37, but without `return` a compiler error should be

    // emitted on line 25

    inout(T)[] opSlice(size_t lower, size_t upper) inout /*return*/

    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]; //BUG: compiler error shoud be emitted here

                                    // if `opSlice` is not decorated with `return`

    }

    T[Len] buf;

    size_t len;

}

​

char[] fun()

{

    char[4] buf = "abcd";

    auto sb = ScopeBuffer!(char, 4)(buf, 4);

    return sb[0..2];  // BUG:  compiler allows data internal to `ScopeBuffer` to 

                      // escape here unless `ScopeBuffer.opSlize` is decorated with `return`

}

​

void main()

{

    auto s = fun();

    writeln(s);

}