What is the difference between $signed and signed' in verilog?

Question

What is the difference between $signed and signed' in verilog?

Answer 1

signed'() does not exist in Verilog. It it exists in SystemVerilog.

IEEE1800-2017 § 6.24.1 Cast operator:

NOTE—The $signed() and $unsigned() system functions (see 11.7) return the same results as signed'() and unsigned'(), respectively.

signed'() exists as feature with casting operator ('())
$signed() exists for compatibility with Verilog