# Nested associative arrays OR associative arrays of dynamic arrays **URL:** \ **Category:** SystemVerilog\ **Tags:** SystemVerilog\ **Created:** [May 2, 2016, 4:31pm UTC](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779 "2016-05-02T16:31:50Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![ravi.ck.kumar](https://verificationacademy.com/forums/letter_avatar_proxy/v4/letter/r/c77e96/32.png) [@ravi.ck.kumar](https://verificationacademy.com/forums/u/ravi.ck.kumar)\ **Post date:** [May 2, 2016, 4:31pm UTC](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779/1 "2016-05-02T16:31:50Z")
Hi Folks, I would like to create an associative array where a string key points to another associative array or to a reference of one. Similarly I would like to create an associative array where a string key points to a dynamic string array. Does the language allow the above data types? -ravi ---
**Author:** ![dave\_59](https://verificationacademy.com/forums/user_avatar/verificationacademy.com/dave_59/32/4499_2.png) [@dave\_59](https://verificationacademy.com/forums/u/dave_59)\ **Post date:** [May 2, 2016, 5:13pm UTC](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779/2 "2016-05-02T17:13:43Z")
\*In reply to [ravi.ck.kumar](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779):\*Yes. SystemVerilog supports arrays whose elements can be of any type. When dealing with dynamically sized array, you can think of it as arrays of arrays instead of multi-dimensional arrays. because an array element in each dimension can have a different number of elements. You can declare arrays of arrays by using an intermediate typedef (preferred) ```verilog typedef int int_index_by_str_t[string]; int_index_by_str_t lookup[]; or int lookup[][string]; ``` ---
**Author:** ![ravi.ck.kumar](https://verificationacademy.com/forums/letter_avatar_proxy/v4/letter/r/c77e96/32.png) [@ravi.ck.kumar](https://verificationacademy.com/forums/u/ravi.ck.kumar)\ **Post date:** [May 2, 2016, 5:26pm UTC](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779/3 "2016-05-02T17:26:01Z")
_In reply to [dave\_59](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779/2):_ Hi David, Thanks for the pointers. Based on that I created a quick example… module mytest(); typedef string AADD[\*]; // create a hash type AADD arrayOfAAs; // create an array of hashes arrayOfAAs AAWC2[string]; // create a hash of ‘array-of-hashes’ \<\<— This Doesn’t. AADD AAWC3[string]; // create a hash of hash. \<\<---- This Works!! … I get the following error. I would like to have a string to reference an array of hashes OR even Error-[SE] Syntax error Following verilog source has syntax error : memory of unknown type “a.sv”, 6: token is ‘;’ arrayOfAAs AAWC2[string]; // create a hash of ‘array-of-hashes’ ---
**Author:** ![dave\_59](https://verificationacademy.com/forums/user_avatar/verificationacademy.com/dave_59/32/4499_2.png) [@dave\_59](https://verificationacademy.com/forums/u/dave_59)\ **Post date:** [May 2, 2016, 6:33pm UTC](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779/4 "2016-05-02T18:33:32Z")
\*In reply to [ravi.ck.kumar](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779/3):\*You need to use a type when declaring a variable. ```verilog typedef AADD arrayOfAAs[]; // create type of an array of hashes arrayOfAAs AAWC2[string]; // create a hash of 'array-of-hashes' ``` or ```verilog AADD arrayOfAAs[]; // create an array of hashes var type(arrayOfAAs) AAWC2[string]; // create a hash of 'array-of-hashes' ``` Also, I do not recommend ever using a wildcard associative array index type. Use an actual type. The wildcard index type is antiquated and cannot be used with a number of other systemverilog features. ---
**Author:** ![ravi.ck.kumar](https://verificationacademy.com/forums/letter_avatar_proxy/v4/letter/r/c77e96/32.png) [@ravi.ck.kumar](https://verificationacademy.com/forums/u/ravi.ck.kumar)\ **Post date:** [May 2, 2016, 6:42pm UTC](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779/5 "2016-05-02T18:42:16Z")
_In reply to [dave\_59](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779/4):_ The second typedef did the trick! Thanks much. Also true about using wildcards. Very little utility in the first place IMHO. ---
**Author:** ![yourcheers](https://verificationacademy.com/forums/letter_avatar_proxy/v4/letter/y/5f9b8f/32.png) [@yourcheers](https://verificationacademy.com/forums/u/yourcheers)\ **Post date:** [May 2, 2016, 11:43pm UTC](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779/6 "2016-05-02T23:43:34Z")
_In reply to [dave\_59](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779/5):_ > \*In reply to [ravi.ck.kumar](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779/5):\*You need to use a type when declaring a variable. ```verilog typedef AADD arrayOfAAs[]; // create type of an array of hashes arrayOfAAs AAWC2[string]; // create a hash of 'array-of-hashes' ``` or ```verilog AADD arrayOfAAs[]; // create an array of hashes var type(arrayOfAAs) AAWC2[string]; // create a hash of 'array-of-hashes' ``` Also, I do not recommend ever using a wildcard associative array index type. Use an actual type. The wildcard index type is antiquated and cannot be used with a number of other systemverilog features. ```verilog AADD arrayOfAAs[]; // create an array of hashes type(arrayOfAAs) AAWC2[string]; // create a hash of 'array-of-hashes' Is this mode of type declaration supported in system-verilog? ``` ---
**Author:** ![dave\_59](https://verificationacademy.com/forums/user_avatar/verificationacademy.com/dave_59/32/4499_2.png) [@dave\_59](https://verificationacademy.com/forums/u/dave_59)\ **Post date:** [May 2, 2016, 11:53pm UTC](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779/7 "2016-05-02T23:53:47Z")
_In reply to [yourcheers](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779/6):_ Yes. See 6.23 Type operator of the 1800-2012 LRM. I forgot to add the **var** keyword in front of the type. I corrected my example. ---
**Author:** ![shlok13](https://verificationacademy.com/forums/letter_avatar_proxy/v4/letter/s/e0b2c6/32.png) [@shlok13](https://verificationacademy.com/forums/u/shlok13)\ **Post date:** [November 6, 2019, 7:33am UTC](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779/8 "2019-11-06T07:33:17Z")
_In reply to [dave\_59](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779/7):_ hi Dave , can we create a typedef using some previous typedef like : typedef enum bit [1:0] {OKAY, ERROR, RETRY, SPLIT} response so i want to create an associative array using response as input and logic [31:0] as key typedef resp\_t address\_driver\_resp [logic [31:0]] ; // will this work ? if yes , how do we register it in our transaction\_item ? ---
**Author:** ![dave\_59](https://verificationacademy.com/forums/user_avatar/verificationacademy.com/dave_59/32/4499_2.png) [@dave\_59](https://verificationacademy.com/forums/u/dave_59)\ **Post date:** [November 6, 2019, 1:27pm UTC](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779/9 "2019-11-06T13:27:45Z")
_In reply to [DV@Engineer](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779/8):_ An associative array can have any element type, and any index type as long as equality is defined for the index type. What do you mean by “register it”? ---
**Author:** ![rlanier1](https://verificationacademy.com/forums/letter_avatar_proxy/v4/letter/r/58f4c7/32.png) [@rlanier1](https://verificationacademy.com/forums/u/rlanier1)\ **Post date:** [August 8, 2024, 4:38pm UTC](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779/10 "2024-08-08T16:38:49Z")
I am unclear by what you mean an array of hashes. Is this the same thing as using a key into an array of arrays? ---
**Author:** ![dave\_59](https://verificationacademy.com/forums/user_avatar/verificationacademy.com/dave_59/32/4499_2.png) [@dave\_59](https://verificationacademy.com/forums/u/dave_59)\ **Post date:** [August 8, 2024, 8:08pm UTC](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779/11 "2024-08-08T20:08:49Z")
People use many different terms for what SystemVerilog calls an _associative array_: map, dictionary, symbol table, or hash. However a _hash_ usually refers to the lookup mechanism used to access an element, not necessarily an array. I tend to avoid it, but was just repeating terminology the previous post used. ---
**Author:** ![prashantg](https://verificationacademy.com/forums/letter_avatar_proxy/v4/letter/p/a9adbd/32.png) [@prashantg](https://verificationacademy.com/forums/u/prashantg)\ **Post date:** [October 4, 2024, 4:37am UTC](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779/12 "2024-10-04T04:37:06Z")
Looks so counter intuitive. ```auto int lookup[][string] ``` feels more like an associative array of dynamic arrays. But it is the other way round. Why is this done? ---
**Author:** ![dave\_59](https://verificationacademy.com/forums/user_avatar/verificationacademy.com/dave_59/32/4499_2.png) [@dave\_59](https://verificationacademy.com/forums/u/dave_59)\ **Post date:** [October 4, 2024, 2:55pm UTC](https://verificationacademy.com/forums/t/nested-associative-arrays-or-associative-arrays-of-dynamic-arrays/31779/13 "2024-10-04T14:55:12Z")
When declaring the 2-dimensional fixed sized array `int A[10][20]`, 10 ius the first dimension and 20 is the second dimension. Selecting `A[0]` gives you a 1-dimensional array of 20 elements. Similarly selecting `lookup[0]` should give you an associative array.