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class Object
# Invokes the public method whose name goes as first argument just like
# +public_send+ does, except that if the receiver does not respond to it the
# call returns +nil+ rather than raising an exception.
#
# This method is defined to be able to write
#
# @person.try(:name)
#
# instead of
#
# @person.name if @person
#
# +try+ calls can be chained:
#
# @person.try(:spouse).try(:name)
#
# instead of
#
# @person.spouse.name if @person && @person.spouse
#
# +try+ will also return +nil+ if the receiver does not respond to the method:
#
# @person.try(:non_existing_method) # => nil
#
# instead of
#
# @person.non_existing_method if @person.respond_to?(:non_existing_method) # => nil
#
# +try+ returns +nil+ when called on +nil+ regardless of whether it responds
# to the method:
#
# nil.try(:to_i) # => nil, rather than 0
#
# Arguments and blocks are forwarded to the method if invoked:
#
# @posts.try(:each_slice, 2) do |a, b|
# ...
# end
#
# The number of arguments in the signature must match. If the object responds
# to the method the call is attempted and +ArgumentError+ is still raised
# in case of argument mismatch.
#
# If +try+ is called without arguments it yields the receiver to a given
# block unless it is +nil+:
#
# @person.try do |p|
# ...
# end
#
# You can also call try with a block without accepting an argument, and the block
# will be instance_eval'ed instead:
#
# @person.try { upcase.truncate(50) }
#
# Please also note that +try+ is defined on +Object+. Therefore, it won't work
# with instances of classes that do not have +Object+ among their ancestors,
# like direct subclasses of +BasicObject+. For example, using +try+ with
# +SimpleDelegator+ will delegate +try+ to the target instead of calling it on
# the delegator itself.
def try(*a, &b)
try!(*a, &b) if a.empty? || respond_to?(a.first)
end
# Same as #try, but raises a NoMethodError exception if the receiver is
# not +nil+ and does not implement the tried method.
#
# "a".try!(:upcase) # => "A"
# nil.try!(:upcase) # => nil
# 123.try!(:upcase) # => NoMethodError: undefined method `upcase' for 123:Fixnum
def try!(*a, &b)
if a.empty? && block_given?
if b.arity.zero?
instance_eval(&b)
else
yield self
end
else
public_send(*a, &b)
end
end
end
class NilClass
# Calling +try+ on +nil+ always returns +nil+.
# It becomes especially helpful when navigating through associations that may return +nil+.
#
# nil.try(:name) # => nil
#
# Without +try+
# @person && @person.children.any? && @person.children.first.name
#
# With +try+
# @person.try(:children).try(:first).try(:name)
def try(*args)
nil
end
# Calling +try!+ on +nil+ always returns +nil+.
#
# nil.try!(:name) # => nil
def try!(*args)
nil
end
end
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