Associative Arrays

Associative arrays are a unique type of array in SystemVerilog. Unlike the previously discussed fixed-size and dynamic arrays that use numerical indices to access elements, associative arrays use a unique key of any data type to access values stored in the array. This key-value pair system makes associative arrays highly versatile and convenient for various design and verification scenarios.

Declaration and Usage

To declare an associative array, you specify the datatype of the elements it will hold, followed by the array name and the datatype of the keys inside square brackets. Here's the basic syntax:

datatype array_name[key_datatype];

For example, to declare an associative array that uses strings as keys and stores integer values:

integer student_scores[string];

In this example, "student_scores" is the associative array that uses student names (strings) as keys to store their scores (integers).

Assigning values to an associative array is simple. You specify the key and the value you want to assign:

student_scores["Alice"] = 85; // Sets the score of "Alice" to 85

To retrieve values from an associative array, use the key:

$display(student_scores["Alice"]); // Will display 85

Characteristics and Use Cases

Associative arrays are particularly useful when the range or number of indices is unknown at compile-time. They offer a lot of flexibility as they can use any datatype as a key, allowing you to create more complex and tailored data structures that can adapt to a wide range of scenarios.

For example, in verification tasks, associative arrays can be useful for storing the results of a testbench where the results need to be associated with non-integer identifiers, or when the results are sporadic and don't map well to a continuous set of indices.

It's important to note that while associative arrays are very flexible, they do have higher memory and computational overhead compared to the other array types. Therefore, they are best used in situations where their unique capabilities provide significant benefits.

In the following section, we will look at the most flexible type of array in SystemVerilog: Queues.