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

[Mannix]

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

[pmallon · Accepted solution]

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[x] is updated.

section at the bottom here on drop in place:

Drop in place

Assign through Drop to delete in place.

q)show d:`a`b`c`x!(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.