Re: Proposal for easier syntax for define-unless-already-defined pattern

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From	Robert Klemme <shortcutter@googlemail.com>
Newsgroups	comp.lang.ruby
Subject	Re: Proposal for easier syntax for define-unless-already-defined pattern
Date	Wed, 30 Jul 2014 19:41:26 +0200
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On 29.07.2014 18:44, Eugene Gilburg wrote:
> Forgot to add, the `?=` syntax should be context-sensitive to
> primitive types. E.g.
>
> some_hash[:some_member] ?= 'some_value'
>
> Should check for `some_hash.key?(:some_value)`

That is unlikely to happen.  The compiler cannot reliably determine that 
some_hash is a Hash for all cases and hence method #key? must be used 
instead of #defined?.

> Which will be assigned if the key does not exist, but not be assigned
> if the key exists but has `false` or `nil` value (another difference
> with the `||=` pattern).

The only way to make that happen is to require the object to also 
implement #key? besides of #[] and #[]= - but then for example Array 
would need this as well.  Which prompts the question what does #key? 
return for in index less than the Array's length where the value stored 
here is nil?

Kind regards

	robert

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Proposal for easier syntax for define-unless-already-defined pattern Eugene Gilburg <eugene.gilburg@gmail.com> - 2014-07-29 09:40 -0700
  Re: Proposal for easier syntax for define-unless-already-defined pattern Eugene Gilburg <eugene.gilburg@gmail.com> - 2014-07-29 09:44 -0700
    Re: Proposal for easier syntax for define-unless-already-defined pattern Robert Klemme <shortcutter@googlemail.com> - 2014-07-30 19:41 +0200
  Re: Proposal for easier syntax for define-unless-already-defined pattern Robert Klemme <shortcutter@googlemail.com> - 2014-07-30 19:45 +0200

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