Return 'this' proposal

Joseph D. Darcy Joe.Darcy at Sun.COM
Tue Mar 17 15:48:26 PDT 2009

Marek Kozieł wrote:
> 2009/3/17 Joseph D. Darcy <Joe.Darcy at <mailto:Joe.Darcy at>>
>     This 'this' proposal remains vague and imprecise.
>     Including this type/self type in a language is a continuing area
>     of study; for example, see the recent paper
>     "Matching ThisType to Subtyping," Chieri Saito and Atsushi
>     Igarashi, Kyoto University, Japan, ACM SAC 2009.
>     There are open bugs requesting this capability. For example typing
>     " <> this type" into a popular
>     search engine quickly yields, amongst other hits,
>     6479372 Add self types (type of 'this' aka ThisClass) to the language
>     This bug discusses the size of the type system impact of this
>     change, a magnitude far too large for Project Coin.
>     There is no need to submit further refinements of this idea; any
>     proposal along the lines of adding a this type will be out of
>     scope for Project Coin.
>     -Joe
> I'll check it, but I'm afraid that introducing 'This' type will be 
> impossible for Java and for all other languages with Inheritance, or I 
> would say it's possible but conditions would be huge.
> return 'this':
> - Idea is quite simple: you use object from left side of dot as 
> returned from method, it's the same quite idea with converting void -> 
> this, but allowed only when it's written directly.
> - Byte-code for that is other story and I'm not sure how much 
> limitation this contains.
> Maybe you cold while what problems you see (that could help)?

As the author and submitter of a proposal, it is your responsibility to 
research, understand, and explain the consequences and implications of 
your proposal.


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