how to monkeypatch Hash's []= method

rubyonrails-talk
1

I'm trying to monkeypatch the = method in the Hash class:

Hash.class_eval do   def _with_feature=(a,b)     puts 'foo'   end   alias_method_chain :=, :feature end

Something is wrong with the syntax, but I can't figure out what. The alias_method_chain method does look for punctuation (= in this case) and expects it to be at the end of the aliased method ( _with_feature=), but I get the following syntax error:

SyntaxError: compile error (irb):5: syntax error, unexpected ')', expecting '=' (irb):7: syntax error, unexpected kEND, expecting ')' (irb):9: syntax error, unexpected kEND, expecting ')'

Any ideas?

Thanks, -H

2

I'm trying to monkeypatch the = method in the Hash class:

doesn't seem to be anything to do with alias_method_chain - just
sticking def _with_feature=(a,b)    puts 'foo' end

into irb causes similar errors. You'll just have to skip alias method
chain this time.

Fred

3

Thanks for the response.

So how in the world is this implemented? The = method’s source code is in C. Other classes override it in a subclass, which works fine, but how would I go about implementing a method that works like the Hash class’ = method?

I’m not sure what you mean by “skipping alias_method_chain” this time. If I do

alias :_without_feature=, := alias :=, :_with_feature

I get the same error, as expected. So how would I go about changing this method’s behavior?

Thanks again, -H

4

Thanks for the response.

So how in the world is this implemented? The = method's source
code is in C. Other classes override it in a subclass, which works
fine, but how would I go about implementing a method that works like
the Hash class' = method?

I'm not sure what you mean by "skipping alias_method_chain" this
time. If I do

alias :_without_feature=, := alias :=, :_with_feature

I get the same error, as expected. So how would I go about changing
this method's behavior?

just call it square_bracket_without feature or something like that.
the problem isn;t the method aliasing it's defining a method called
_with_feature=

Fred

5

I was focusing on the “=” being the problem… Worked nicely. Many thanks!