File actionpack/lib/action_controller/metal/flash.rb, line 12
def redirect_to(options = {}, response_status_and_flash = {}) #:doc:
if alert = response_status_and_flash.delete(:alert)
flash[:alert] = alert
end
if notice = response_status_and_flash.delete(:notice)
flash[:notice] = notice
end
if other_flashes = response_status_and_flash.delete(:flash)
flash.update(other_flashes)
end
super(options, response_status_and_flash)
end
And I thought: ouch, aren’t those supposed to be double-equals? Well,
no, it’s an assignment within an if statement. It saves a line of
code per usage, thus three lines of code in that method.
But I thought: wow, that sure violates the principle of least
surprise. Perhaps it would be nice if there were a way to reference
the most recent if-expression. I recall how a lone underscore in irb
will contain the value of whatever was last evaluated. So perhaps
something like this would be nice:
if response_status_and_flash.delete(:notice)
flash[:notice] = _
end
instead of what we see above:
if notice = response_status_and_flash.delete(:notice)
flash[:notice] = notice
end
end
code per usage, thus three lines of code in that method.
instead of what we see above:
if notice = response_status_and_flash.delete(:notice)
flash[:notice] = notice
end
Interesting, but I think using _ is even more surprising isn’t it? What
happens when you have this…
if something-that-returns-a-value-and-passes-the-if-test
if something-that-returns-a-value-but-fails-the-if-test
# never happens
else
# what does _ reference? The very top level if? Or the second one?
# Both were evaluated, but one failed so does it count towards _ or
not?
# How do I access the first _ if Ruby decides _ is the second one?
end
end
end
code per usage, thus three lines of code in that method.
But I thought: wow, that sure violates the principle of least
surprise.
In that situation I would code it as
if ( other_flashes = response_status_and_flash.delete(:flash) )
which arguably makes the intention clearer with only a few extra
characters an no run time penalty.
assuming that the intent is to call
response_status_and_flash.delete(:notice) just once, test the result,
and then use a truthy result in the flash[:notice], this is almost
exactly what I typically type.
However, I’d really put ( ) around the expression.
if (notice = response_status_and_flash.delete(:notice))
flash[:notice] = notice
end
This is a trick from JSLint which will complain about assignments in
the conditional expression of an if, but an extra pair of parentheses
will signal your intent and silence the warning.
