Ruby if .. elsIf .. else on a single line?

Question

With the ruby ternary operator we can write the following logic for a simple if else construct:

a = true  ? 'a' : 'b' #=> "a"

But what if I wanted to write this as if foo 'a' elsif bar 'b' else 'c'?

I could write it as the following, but it's a little difficult to follow:

foo = true
a = foo  ? 'a' : (bar ? 'b' : 'c') #=> "a"

foo = false
bar = true
a = foo  ? 'a' : (bar ? 'b' : 'c') #=> "b"

Are there any better options for handling such a scenario or is this our best bet if we wish to condense if..elsif..else logic into a single line?

I think the problem with the lack of readability in the nested ternary solution is that putting all of this on one line is inherently difficult to read, and none of the solutions you come up with are going to be much easier to parse. — John Biesnecker, Dec 12 '12 at 21:27
In other words, with more experience you will learn that squeezing as much code into as small a space as possible is never a valid goal. — Ed S., Dec 12 '12 at 21:34
"squeezing as much code into as small a space as possible is never a valid goal." except in machine-code. — the Tin Man, Dec 12 '12 at 22:24

score 54 · Accepted Answer · answered Dec 12 '12 at 21:25

54

a = (foo && "a" or bar && "b" or "c")

or

a = ("a" if foo) || ("b" if bar) || "c"

answered Dec 12 '12 at 21:25

sawa

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Interest answer, Sawa. Is this using `or` precedence as a trick? – sunnyrjuneja Dec 12 '12 at 21:27
2

`or` and `and` have lower associativity than `&&` and `||`. – sawa Dec 12 '12 at 21:29
2

I love this...`and` and `or` are friends as long as you learn precedence, which everyone should. – Casey Foster Dec 12 '12 at 21:30
This won't work if the value you want to return is falsey. `irb(main):001:0> a = (false if true) || ("b" if true) => "b"` – Trevor McCasland Oct 10 '19 at 15:54

sunnyrjuneja · Answer 2 · 2017-09-25T19:07:23.187

20

The Github Ruby Styleguide recommends that one liners be reserved for trivial if/else statements and that nested ternary operators be avoided. You could use the then keyword but its considered bad practice.

if foo then 'a' elsif bar then 'b' else 'c' end

You could use cases (ruby's switch operator) if find your control statements overly complex.

edited Sep 25 '17 at 19:07

answered Dec 12 '12 at 21:26

sunnyrjuneja

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`if foo then 'a' elsif bar then 'b' else 'c'` No need for the semi colon after bar – UsamaMan Sep 23 '17 at 16:37
thanks for the suggestion, editting to remove it now – sunnyrjuneja Sep 25 '17 at 00:42
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I forgot `end` after `c`. We need to add that too. – UsamaMan Sep 25 '17 at 02:58

score 5 · Answer 3 · answered Dec 12 '12 at 21:25

5

a = if foo then 'a' elsif bar then 'b' else 'c' end

answered Dec 12 '12 at 21:25

tjmw

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tokland · Answer 4 · 2017-04-18T20:43:48.663

3

You can also write:

x = if foo then 'a' elsif bar then 'b' else 'c' end

However, this isn't idiomatic formatting in Ruby.

edited Apr 18 '17 at 20:43

answered Dec 12 '12 at 21:23

tokland

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Ruby if .. elsIf .. else on a single line?

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