问题
why is an assign statement more efficient than not using assign?
co-workers say that:
assign
a=3
v=7
w=8.
is more efficient than:
a=3.
v=7.
w=8.
why?
回答1:
You could always test it yourself and see... but, yes, it is slightly more efficient. Or it was the last time I tested it. The reason is that the compiler combines the statements and the resulting r-code is a bit smaller.
But efficiency is almost always a poor reason to do it. Saving a micro-second here and there pales next to avoiding disk IO or picking a more efficient algorithm. Good reasons:
0) Back in the dark ages there was a limit of 63k of r-code per program. This was a way to reduce the size of r-code and stay under that limit (ok, that might not be a "good" reason). One additional way this helps is that you could also often avoid a DO ... END pair and further reduce r-code size.
1) When creating a record the fields that are part of an index will be written back to the database as they are assigned (not at the end of the transaction) -- grouping all assignments into a single statement helps to avoid inconsistent dirty reads. (This is probably the best reason to still do it.)
2) Readability -- you can argue that grouping consecutive assignments more clearly shows your intent and is thus more readable. (I like this reason but not everyone agrees.)
回答2:
ASSIGN will combine multiple statements into one. If a, v and w are fields in your db, that means it will do something like INSERT INTO (a,v,w)...
rather than INSERT INTO (a)... INSERT INTO (v)
etc.
回答3:
basically doing:
a=3.
v=7.
w=8.
is the same as:
assign a=3.
assign v=7.
assign w=8.
which is 3 separate statements so a little more overhead. Therefore less efficient.
来源：https://stackoverflow.com/questions/17109045/what-is-the-efficiency-of-an-assign-statement-in-progress-4gl