Is this similar to function alias?

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1

I am studying the official example code from here: https://github.com/kxcontrib/websocket/blob/master/AppendixB/pubsub.q . After playing around for a while, I can get the publisher/subscriber model work but still I don’t understand what exactly this line (https://github.com/kxcontrib/websocket/blob/ad2f0b268afaee1fc5f4dda2fc2467440c7e2f0c/AppendixB/pubsub.q#L8) is doing.

After checking the Reference card (https://code.kx.com/q/ref/), I know that insert is a built-in function and Overloaded glyphs (https://code.kx.com/q/ref/overloads/) says that : (colon) only has two possible meanings (https://code.kx.com/q/ref/overloads/#colon).

 

So here comes the question, what does

upd:insert;

do? Does it mean that we declare upd as an alias of insert, so calling upd will be exactly the same as calling insert? (But I did try it myself, eliminating this line and directly call insert here: https://github.com/kxcontrib/websocket/blob/ad2f0b268afaee1fc5f4dda2fc2467440c7e2f0c/AppendixB/fh.q#L18-L19, no, it doesn’t work lol)

2

Yes defining upd in this way means it behaves the same as insert (mostly)

 

q)upd:insert q)tab:( a:1 2) q)insert[tab;enlist 3] ,2 q)tab a - 1 2 3 q)upd[tab;enlist 4] ,3 q)tab a - 1 2 3 4

 

But there are differences. ‘insert’ is a built in operator which cannot be passed as the first item by reference over a handle.

(This is causing the issue you are seeing)

 

q)value(upd;tab;enlist 5) //Pass by reference succeeds for user defined function ,4 q)value(insert;tab;enlist 6) //Pass by reference fails for operator 'insert [0] value(insert;tab;enlist 5) ^ q)value(“insert”;tab;enlist 6) //Pass as parse string succeeds ,5 q)value(insert;tab;enlist 6) //Pass by value succeeds ,6

 

 User defined functions can only use prefix notation whereas operators can be used prefix or infix.

 

q)tab insert enlist 7 //Infix with operator succeeds ,7 q)tab upd enlist 8 //Infix with user defined function fails 'type [0] tab upd enlist 8 ^ q)insert[tab;enlist 8] //Prefix with operator succeeds ,8 q)upd[`tab;enlist 9] //Prefix with user defined function succeeds ,9