interpolating a string to part of a ruby method

Question

I have items that can be one of several attributes like red, yellow, green (more complex than this) and they have corresponding is_red, is_yellow, is_green booleans.

I'd like to have an api function to change this value where I pass for example:

id: 12
type: red

in my function have:

item=Item.find(id)
if item.is_ + type == true
  item.is_ + type=false
end

How would I do this?

thx in advance

Don't. Have a single attribute called Color and a method is_color(color) instead. — verdesmarald
– verdesmarald, Commented Oct 2, 2012 at 1:00
thx, as mentioned in question, it is more complex than just colors (in fact doesn't involve colors). — timpone
– timpone, Commented Oct 2, 2012 at 1:02
I can't think of a single use case where this would be a good idea, even not involving colors. — Mark Thomas
– Mark Thomas, Commented Oct 2, 2012 at 1:18
legacy system with well constructed graphs of data. works really well — timpone
– timpone, Commented Oct 2, 2012 at 1:39
The question states "variable names" bit the example code references method calls. — Mars
– Mars, Commented Oct 2, 2012 at 5:42

Benoît · Accepted Answer · 2012-10-02 00:59:41Z

6

Use send

item = Item.find(id)

if item.send(:"is_#{type}") == true
  item.send(:"is_#{type}=", false)
end

answered Oct 2, 2012 at 0:59

Benoît

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1 Comment

Wayne Conrad Over a year ago

Send will take either a string or a symbol, so the colons could be omitted if desired.

Mars · Accepted Answer · 2012-10-02 05:39:36Z

-1

You cannot build variable names dynamically in Ruby without using eval, which would be dirty, but functional.

You could use method_missing on a BlankSlate object to capture free text method calls and handle them as a big dirty case statement.

The most elegant solution would be a Hash, because keys can be easily composed dynamically.

answered Oct 2, 2012 at 5:39

Mars

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