What is the purpose of the underscore in this line of u.q

Community Support
1

In the u.q file of the following set up, what is the purpose of the underscore here, (It doesn’t appear to me to be cut or drop) 

del:{w_:w[x;;0]?y};.z.pc:{del[;x]each t};

2

Hi,

it is drop in place to modify the dictionary w of table subscriptions. It is checking the list of subs for table x, for handle y, if there is an item it’s dropped from the list and w is updated.

section at the bottom here on drop in place:

Drop in place

Assign through Drop to delete in place.

q)show d:abcx!(1;2 3;4;5) a| 1 b| 2 3 c| 4 x| 5 q)d _:`x q)d a| 1 b| 2 3 c| 4

Hope that helps, if not let me know.