The Ruby Way: Solutions and Techniques in Ruby Programming, Second Edition

2.22. Delayed Interpolation of Strings

Sometimes we might want to delay the interpolation of values into a string. There is no perfect way to do this. One way is to use a block:

str = proc {|x,y,z| "The numbers are #{x}, #{y}, and #{z}" }

s1 = str.call(3,4,5)   # The numbers are 3, 4, and 5
s2 = str.call(7,8,9)   # The numbers are 7, 8, and 9

A more heavyweight solution is to store a single-quoted string, wrap it in double quotes, and evaluate it:

str = '#{name} is my name, and #{nation} is my nation'
name, nation = "Stephen Dedalus", "Ireland"
s1  = eval('"' + str + '"')
# Stephen Dedalus is my name, and Ireland is my nation.

It’s also possible to pass in a different binding to eval:

bind = proc do name,nation = "Gulliver Foyle", "Terra" binding ...