ruby - Why does a variable that gets assigned inside a Proc not persist over repeated calls of the Proc? -


ruby 1.9.2 code:

def append_string_to_text(string_to_append)   string_to_alter = 'starting_bit'   p "outside block: string_to_alter.object_id #{string_to_alter.object_id}"   proc.new     p "****** start of block: string_to_alter.object_id #{string_to_alter.object_id}"     p "defined?(new_string_created_in_block) #{defined?(new_string_created_in_block) == true}"     unless defined?(new_string_created_in_block)       p "new_string_created_in_block undefined. lets define it."       new_string_created_in_block = 'test'     end     p "new_string_created_in_block.object_id #{new_string_created_in_block.object_id}"     string_to_alter = string_to_alter + string_to_append     p "end of block: string_to_alter.object_id #{string_to_alter.object_id}"     string_to_alter   end end  proc = append_string_to_text('_text_at_the_end') p proc.call p proc.call

output:

"outside block: string_to_alter.object_id 70283335840820" "****** start of block: string_to_alter.object_id 70283335840820" "defined?(new_string_created_in_block) false" "new_string_created_in_block undefined. lets define it." "new_string_created_in_block.object_id 70283335840520" "end of block: string_to_alter.object_id 70283335840440" "starting_bit_text_at_the_end" "****** start of block: string_to_alter.object_id 70283335840440" "defined?(new_string_created_in_block) false" "new_string_created_in_block undefined. lets define it." "new_string_created_in_block.object_id 70283335840180" "end of block: string_to_alter.object_id 70283335840100" "starting_bit_text_at_the_end_text_at_the_end"

the first time block run, string_to_alter variable points object created @ start of append_string_to_text method, because block closure. block creates new variable new_string_created_in_block, , creates new block local variable string_to_alter, shadowing outer variable string_to_alter.

the second time block run, string_to_alter variable points object created during first time block run.

why during second run, new_string_created_in_block undefined? gets assigned during first run, , assigning of string_to_alter variable gets persisted first run, why doesn't new_string_created_in_block persist well?

string_to_alter gets persisted because it's outside of proc block , part of closure. proc block gets instantiated @ each invocation, however, hence lack of persistence of of variables defined within block.


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