Are SystemVerilog arrays passed by value or reference?

Question

By default, is SystemVerilog passing arrays by value or reference?

For instance:

int array[5] = '{0,1,2,3,4}; some_function(array); // <-- value or reference? 

Answer 1

By default, SystemVerilog passes arrays by value, copying the entire array.

It is recommended that you use arrays by reference, if possible for performance reasons.

• If you want your function to modify the array, use ref .
• If you want your function to read an array, use const ref .

Example:

  function void pass_by_value(int array[5], int queue[$], int assoc[int]); // Default. // A copy of the arrays is made in this function endfunction function void pass_by_ref(ref int array[5], ref int queue[$], ref int assoc[int]); // Original arrays are being referenced endfunction function void pass_by_const_ref(const ref int array[5], const ref int queue[$], const ref int assoc[int]); // Original arrays are being referenced // And they can be read but cannot be modified in this function endfunction 

Example on EDA Playground: http://www.edaplayground.com/x/2m9