Problem with attributes method OR send method?

Question

This line of code:

@instance.attributes.each{|key, value| @instance.send(key) = nil}

yields this error:

syntax error, unexpected '=', expecting '}'

I'm having trouble understanding why that is.. When I write something like:

@instance.attributes.each{|key, value| puts @instance.send(key)}

it behaves as expected, outputting the value of each attribute. Why does it work as a getter but not as a setter in this context? Is there a problem with my syntax?

Thanks a lot.

BTW, if @instance is an ActiveRecord instance, you could use @instance[key] = nil, see ActiveRecord::AttributeMethods#[]= — Stefan
– Stefan, Commented Apr 2, 2019 at 16:03
I could have sworn that that was the first thing I tried, but right you are. Thanks a lot. — Josh Kestenberg
– Josh Kestenberg, Commented Apr 2, 2019 at 16:34

jvillian · Accepted Answer · 2019-04-02 15:19:40Z

3

@instance.send(key)

Is calling the getter method. To call the setter method, try:

@instance.attributes.each{|key, value| @instance.send("#{key}=", nil)}

answered Apr 2, 2019 at 15:19

jvillian

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4 Comments

Josh Kestenberg Over a year ago

This worked. Thanks a lot. Why is it that I can ordinarily call a setter method without using this syntax? eg @instance.attribute = nil rather than @instance.attribute=(nil)

jvillian Over a year ago

That's a good question. I don't know the precise answer and hesitate to speculate. I suppose some digging through the source code would likely reveal the answer. Or, one of the gurus may swing by and tell us why. Apologies!

Stefan Over a year ago

@JoshKestenberg it's called syntactic sugar. The parser detects certain structures and converts them, so you can write @instance.attribute = nil to invoke a setter, or 1 + 2 instead of 1.+(2).

jvillian Over a year ago

@Stefan - Great explanation. Thanks!

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