Dynamically create an escaped constant (Ruby on Rails)

Question

I need to dynamically create a constant that is escaped out of the current namespace, so I need the '::' in front of my constant. However, when I try the below, I get the below error...

def make_constant(type)     
  "::"+"#{type}".singularize.camelize.constantize
end

When I try some thing like

make_constant("MyModel") the result should be a constant of:

::MyModel

However, I get and error:

TypeError (no implicit conversion of Class into String)

I don't think their should be a "metaprogramming" tag. – Cary Swoveland Sep 04 '19 at 22:37 — Cary Swoveland, Sep 04 '19 at 22:37

mrzasa · Accepted Answer · 2019-09-05T07:04:19.890

3

In Ruby + has lower priority than method invocation ., so you first create a class with "#{type}".singularize.camelize.constantize and then you try to add this class to a string '::' that fails.

To fix it you can:

("::"+"#{type}".singularize.camelize).constantize # ugly, but proves the point
"::#{type.singularize.camelize}".constantize #elegant and working :)

edited Sep 05 '19 at 07:04

answered Sep 04 '19 at 22:03

mrzasa

22,895
11
56
94

The elegant option does not work because camelize does not operate the same way as the top version. – user2012677 Sep 04 '19 at 22:07
thanks @user2012677 fixed that by moving it inside the interpolation – mrzasa Sep 05 '19 at 07:05

score 0 · Answer 2 · answered Sep 05 '19 at 00:13

0

You should not need to concatenate or use parens on the method chain

def make_constant type
  "::#{type}".singularize.camelize.constantize
end

answered Sep 05 '19 at 00:13

lacostenycoder

10,623
4
31
48

"::word".camelize = "::word", where "::"+'word'.camelize = ::Word – user2012677 Sep 05 '19 at 02:05

Dynamically create an escaped constant (Ruby on Rails)

2 Answers2