Feature #6561

?= operator

Added by Vlad Moskovets over 3 years ago. Updated about 3 years ago.



I have feature proposition to add new opearator ?= its like ||= but assigns only when variable is not defined
So it should be shortcut for

@var ?= 1


defined?(@var) ? @var : @var = 1

It should useful for caching nil'able or false'able items

Related issues

Duplicates Ruby trunk - Feature #6023: Add "a ?= 2" support for meaning "a = a.nil? ? 2 : a" Rejected 02/15/2012


#2 Updated by Rodrigo Rosenfeld Rosas over 3 years ago

Would this be valid only for instance variables or any variable?

#3 Updated by Nobuyoshi Nakada over 3 years ago

rosenfeld (Rodrigo Rosenfeld Rosas) wrote:

Would this be valid only for instance variables or any variable?

Only for instance variables, class variables, and global variables.
"undefined local variable" makes no sense.

#4 Updated by Rodrigo Rosenfeld Rosas over 3 years ago

exactly, I was just wanting to make sure. My other proposition for ?= would work for local variables as well, although it would always evaluate the expression if the current value is null while this proposition will only evaluate it once.

For example, suppose a method like this:

def my_method something = nil, something_else = nil
my_var = something || something_else
my_var ?= begin

Yeah, I know we could do "... || something_else || begin", but #6023 would allow false values to prevent the begin-end block execution.

The other approach would be something like:

my_var = begin
end if my_var.nil?


if my_var.nil?
my_var = begin

I'm not strictly defending #6023 because I don't remember needing something like this yet (that's why I couldn't think in a concrete example) as what motivated me to ask for such feature was to be able to cache "false" values in my instance variables, so both #6023 and #6561 would work for me.

I'm just stating what are the major differences between them...

#5 Updated by Yutaka HARA about 3 years ago

  • Target version changed from 2.0.0 to next minor

#6 Updated by Nobuyoshi Nakada about 3 years ago

  • Status changed from Open to Rejected

I'm not against this feature concept, but '?=' conflicts with existing syntax.
You have to propose different syntax.

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