When there are only two states for instance variable "a", either it has a value or not, and there is only one possible state for instance variable "b", it has a value. I can set "a" equal to "b" if "a" does not have a value via:
@a = nil
@b = "world"
def set_a
@a ||= @b
end
set_a
p @a
=> "world"
@a = "hello"
@b = "world"
def set_a
@a ||= @b
end
set_a
p @a
=> "hello"
But, what if there is more than one option for "a" to be set to? For example, I want to set instance variable "a" to either "b" or "c" depending on which has a value. In the program, only either "b" or "c" will have a value, always one but never both. Is there a way, using operators to write something like the following:
if @a == nil
if @b == nil
@a = @c
else
@a = @b
end
end
I was trying to write something that looks like this:
def set_a
@a ||= (@b || @c)
end
But, if @a had a value it would remain. Which is what I want. However, if @a was nil, then it would not take on the value of either @b or @c, it would remain nil.
Thank you for you time.
You can write
Module.const_defined?(:A) ? A : (B == true ? B : C)
to obtain the value of A.
A not defined
B = true
Module.const_defined?(:A) ? A : (B == true ? B : C)
#=> true
A not defined
B = false
Module.const_defined?(:A) ? A : (B == true ? B : C)
#=> 42
A = "cat"
B = false
C = 42
Module.const_defined?(:A) ? A : (B == true ? B : C)
#=> "cat"