System Verilog Nested Associative Array

Question

How do you declare and initialize a nested associative array in SystemVerilog?

/*
  Creating an associative array(AA) called timings such that
  each key contains an AA with a list of relevant key value pairs
*/
typedef string timingObj [string];
timingObj timings [string] = {"A": {"B" : "C"}, "X": {"Y" : "Z"} };
//string timings [timingObj] = {"A": {"B" : "C"}, "X": {"Y" : "Z"} }; //Same error

timingObj t;
$cast(t, timings["A"]); // t = {"B" : "C"}
$display("%s", timings["A"]);
$display("%s", t["B"]);

The code above results in compiler errors:

"Syntax error. Unexpected token: }. Expected tokens: ':'." "testbench.sv" 2
"Syntax error. Unexpected token: $cast[_SYSTEM_CAST]. Expected tokens: ';' , 'checker' , 'function' , 'task' , 'timeprecision' ... ." "testbench.sv" 6  6

dave_59 · Accepted Answer · 2019-04-16 16:05:54Z

3

Assignment patterns for associative arrays need a '{} mark in front to distinguish it from a concatenation {}. There are some cases where it is ambiguous (but not here). So write

timingObj timings [string] = '{"A": '{"B" : "C"}, "X": '{"Y" : "Z"} };

answered Apr 16, 2019 at 16:05

dave_59

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6 Comments

Julito Sanchis Over a year ago

Good thing i cleaned the code a bit, then how would you access each individual key? the $cast function returns an error, is it even required?

dave_59 Over a year ago

$cast is only needed for certain class variable assignments and when you are not sure of the variable type because of type parameterization. You should be able to write t = timings["A"];

Julito Sanchis Over a year ago

and finally.... $display("%s", t["B"]); to access the nested variable?

dave_59 Over a year ago

timings["A"] is not a string, is an associative array of strings. Use %p instead of %s

Julito Sanchis Over a year ago

I hate to be pedantic, t = timings["A"];$display("%p", t["B"]); displaying "C" but instead it returns a new error "Syntax error. Unexpected token: t[_IDENTIFIER] ..."

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