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

Academy Support
1

https://learninghub.kx.com/forums/topic/what-is-the-purpose-of-the-underscore-in-this-line-of-u-q

In the u.q file of the following set up, what is the purpose of the underscore here, (It doesnt 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 its 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:`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.