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Feature #11361
openproposal for easy method to nil-guard for generated variable name.
Status:
Open
Assignee:
-
Target version:
-
Description
It's easy to 'nil-guard' for normal variable.
def user
@user ||= User.find(1)
end
but it's not simple for generated variable name.
def user(id)
variable_name = "@user_#{id}"
instance_variable_set(variable_name, User.find(id)) unless instance_variable_defined?(variable_name)
instance_variable_get(variable_name)
end
I want to write it like this.
def user(id)
instance_variable_get_or_set("@user_#{id}") { User.find(1) }
end
it can be implemented by this code.
def instance_variable_get_or_set(variable_name, &block)
instance_variable_set(variable_name, block.call) unless instance_variable_defined?(variable_name)
instance_variable_get(variable_name)
end
Updated by marcandre (Marc-Andre Lafortune) over 9 years ago
Isn't this simpler (and easier to read):
@cache ||= {}
@cache[id] ||= User.find(1)
I can't recall ever needing to do what you want to do.
Updated by jwmittag (Jörg W Mittag) almost 9 years ago
masaki yamada wrote:
It's easy to 'nil-guard' for normal variable.
def user @user ||= User.find(1) end
but it's not simple for generated variable name.
def user(id) variable_name = "@user_#{id}" instance_variable_set(variable_name, User.find(id)) unless instance_variable_defined?(variable_name) instance_variable_get(variable_name) end
Note that the two examples you gave are not equivalent: the first assigns to the variable if it evaluates to false
or nil
regardless of whether it is defined or not, the second only assigns if it is undefined. Which one of the two do you want?
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