CODEWITHSUNDEEP
variablesluametasyntactic-variable
Pwrcdr87
Pwrcdr87

Reputation: 965

Why set underscores equal to a function?

I've searched for an answer here and elsewhere online, but all topics deal with either iterating a table, metatables, or times when _,var1 = do_some_stuff() which are not the case here.

This is just a non-realistic function, but containing examples of what I mean:

function do_some_stuff(data)
    _ = some_function(data)
    some_other_code
    _ = some_other_function(data)
end

Wouldn't this be considered the same as simply entering:

function do_some_stuff(data)
    some_function(data)
    some_other_code
    some_other_function(data)
end

I know that if I create a basic Lua program like this both versions run the same:

function hello(state)
    print("World")
end

function ugh(state)
    _ = hello(state) -- and w/ hello(state) only
end

ugh(state)

I just would like to know if there can be a time where this _ = some_function() is necessary?

Upvotes: 3

Views: 890

Answers (2)

lyravega
lyravega

Reputation: 101

In the example you wrote, _ is meaningless. In general, _ is used if a function is returning multiple values, and you don't need all of the returned stuff. A throw-away variable _ is, so to speak.

For example: 

local lyr, needThis = {}
lyr.test = function()
    local a, b, c;
    --do stuff
    return a, b, c
end

Lets say, for such a function that returns multiple values, I only need the 3rd value to do something else. The relevant part would be:

_, _, needThis = lyr.test()

The value of needThis will be the value of c returned in the function lyr.test().

Upvotes: 3

Pwrcdr87
Pwrcdr87

Reputation: 965

There is no benefit to _ = do_some_stuff(), rather using do_some_stuff() is fine and more accepted. The underscore provides no benefit when used in this way.

Thanks Etan Reisner and Mud for the help and clarification.

Upvotes: 2

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