Champion "defer statement"

[gafter]

See #513

• Proposal added
• Discussed in LDM
• Decision in LDM
• Finalized (done, rejected, inactive)
• Spec'ed

This is to be considered alongside #1174 (though we could elect to do one without the other)

[alrz]

This is to be considered alongside #1174 (though we could elect to do one without the other)

I guess this has been brought up before but just to mention, #1174 + "convention-based Dispose" could address the use cases for a "defer statement" (edit: except that it's not anything like resource cleanup, which I believe, such language construction would encourage).

[HaloFour]

@alrz That would be #93

[gafter]

@alrz #1174 + "convention-based Dispose" doesn't help much as a replacement for defer, as it requires creating an object. defer would not create any runtime garbage.

[scalablecory]

I feel like, outside of calling Dispose (for which there are better proposals), this would be so rarely used that I can't really make a case for its inclusion in the language.

I also think it's very easy to misuse. Not always the case, but generally if you have more than one cleanup block in your code it's a code smell.

#1174 seems much easier for users to use correctly from the standpoint of separation of concerns.

[alrz]

One valid use case that I can think of, is to save the current state in traversal of some tree structure and reverting back that state once all children are visited.

Still, since this feature is really easy to abuse, I think as long as we keep it undocumented we're fine.

[gafter]

In the spirit of designing the language for myself, there are hundreds of places in the compiler where this would be a simplification of existing code.

[yaakov-h]

@gafter wouldn't "convention-based Dispose" plus a struct similarly not create an object?

[gafter]

@yaakov-h Sure you can do that. And you're going to store a delegate in the struct I presume so you can pass a lambda with your arbitrary code in it?

[yaakov-h]

@gafter #302? 😄

[gafter]

Static delegates cannot capture anything

[tannergooding]

@gafter, static delegates by themselves don't capture anything (as proposed).

This does not, however, mean the compiler could not create some struct which allowed state to be carried and passed to a static delegate when invoked (such as to support some other feature).