ruby more than 2 alternative in or-operator

Question

I have this line of code:

if self.include?("van " || "de " || "von ")

why doesn't the block included after this line execute when the third alternative of the or-operator is true?

When my string is "von wartburg" the block doesn't execute, but when my string contains "van" or "de" then it does.

"or 'de' then it does" - nope. it works only for "van" – Sergio Tulentsev Mar 05 '17 at 15:48 — Sergio Tulentsev, Mar 05 '17 at 15:48
thanks for the English language corrections ;) – thiebo Mar 06 '17 at 09:22 — thiebo, Mar 06 '17 at 09:22

Andrey Deineko · Accepted Answer · 2017-03-05T15:51:33.563

3

self.include?("van " || "de " || "von ")

Will ALWAYS evaluate to

self.include?("van ")

Why? Because of how || works.

"van " || "de " || "von "
# ↑↑↑↑↑↑ evaluates to "van " and does not give a slightest shoe about the rest

See String#include - it accepts a substring and offset as arguments.

What you need is the following:

["van ", "de ", "von "].any? { |substring| self.include?(substring) }

edited Mar 05 '17 at 15:51

answered Mar 05 '17 at 15:46

Andrey Deineko

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score 1 · Answer 2 · edited May 23 '17 at 12:32

1

The 'or' will always evaluate "van " because of how || works.

Try using a regular expression like:

self =~ /^(van\ |de\ |von\ )/

edited May 23 '17 at 12:32

Community

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answered Mar 05 '17 at 15:51

Navarro

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score 0 · Answer 3 · answered Mar 05 '17 at 15:46

0

I think what you want is

if self.include?("van ") || self.include?("de ") || self.include?("von ")

Having the || inside the call to include? makes it only evaluate the first string. You want to test include? for each case.

answered Mar 05 '17 at 15:46

River

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score 0 · Answer 4 · edited Mar 05 '17 at 17:06

Well it doesn't work for "de " either

2.3.0 :004 > "van test".include?("van " || "de " || "von ")
 => true
2.3.0 :005 > "de test".include?("van " || "de " || "von ")
 => false
2.3.0 :006 > "von test".include?("van " || "de " || "von ")
 => false

When you run String#include?("van " || "de " || "von ") you pass only one argument to the function: "van " || "de " || "von ".

Boolean OR (||) will return the first element of the list that evaluates to true. So this is strictly identical to String#include?("van ").

I know only two ways to do what you were trying to do in just one line :

You can make a table of substrings to test and use any? over it

["van ", "de ", "von "].any? { |s| string.include?(s) }
Or you can use a regex (in which the or operator (|) does exactly what you want)

/van |de |von / =~ string

ruby more than 2 alternative in or-operator

4 Answers4