SV Implementation of dynamic array of memory?

Hi Friends,
     I want to implement a buffer where I can insert & delete an element flexibly. What I mean to say is something similar to keyed list in specman, I want to implement in SV CB methodology using URM.
   I tried using dynamic memory but I failed creating "new address"(suppose address as my key) for every element I want to add at every other instant of time.

rand int buffer[];
int j = 0;

task ins_element(input [31:0] data);
buffer[j] = new;
buffer[j] = data;
j++;
endtask

Note:  I don't want STACK or FIFO type of implementation here where the array length of memory is static

Here the error is "The function new cannot be used to creat an object to assign to this variable"
Can anyone help me in this regards so as to suggest me how to proceed?

Thanks in advance,
Jalli