Function isOnStack

test/doctest.h:611–611

    char* allocate(size_type sz);

    bool isOnStack() const noexcept { return (buf[last] & 128) == 0; }
    void setOnHeap() noexcept;
    void setLast(size_type in = last) noexcept;
    void setSize(size_type sz) noexcept;