Verilog assigment and replication , What do the parenthesis do?
{1 {(address == 0)}} is unusually because there is no replication. It could easily be written as (address == 0) and have the same result. A more readable form would be:

assign read_mux_out = (address == 0) ? data_in : (address == 1) ? data_dir : 1'b0;


My guesses why it was written this way:


At some point in time (or anticipating in the future) data_in and data_dir were (or may become) multi-bit vectors. In which case it is used for making scaling easier. But if I were to write it this way for future proofing, I'd use a parameter
The author maintaining a coding style. I cannot see the rest of the code, but perhaps there are places where the replicator makes sense


The only rational reason I can think of why the author use bitwise operations (&amp;,|) indeed of conditional operators (?:) is if the target synthesizer poorly optimized conditional operators (I've seen this even in some modern high-end synthesizers) and it is a critical data path. There are defiantly cleaner ways of writing the code.