Warp wrote:
>   The 'defer' feature sounds a lot like reinventing the RAII mechanism,
> the hard way.

Worse in some ways, better in others. For example, I don't know any way to 
use RAII to conditionally modify the return value of the function you're 
returning from in the event of an error. Also, you can't run a destructor 
inside an "if" statement - scopes nest statically, not dynamically.

On the other hand, if you *are* using it for resource management, you have 
to remember to write it everywhere you allocate the resource. The solution 
there, methinks, would be to put more resources under management.

Defer doesn't introduce a scope, so you can invoke it from inside a 
conditional or a loop.

On the other hand, defer always runs at the end of the function in which it 
was called, so you can't use it easily inside a library function where you 
want it to run when the method calling the library entrypoint returns.

Defer takes a lambda, so it can easily refer to local values from the 
function that called it when it runs. You'd have to use pointers to autos 
stored in the RAII class that get dereferenced in the destructor to do 
something like that in C++.

>   Also, I can't really understand how 'panic' and 'recover' are different
> from regular 'throw' and 'catch' in almost any other language.

Again, it's because they're not control flow statements. "panic" is pretty 
much identical to "throw" except it confusingly looks like a function 
instead of a statement, so you have special cases in the wrong place in the 
compiler as it does control flow analysis. (I.e., in much the same way that 
old C compilers might complain about a function that ends with "exit()" 
inside a conditional not returning a value from that branch.)

Recover can be inside a conditional, just like defer can. On the other hand, 
most variants of "catch" have something equivalent to "re-throw", so...

It's also not obvious to me that any sort of stack trace gets passed up, so 
if you're trying to debug why it's panicing, it isn't clear to me you can 
manage that. I suspect once you "recover" a panic, you're pretty much 
screwed in terms of debugging if you recovered a panic you didn't expect.

Everything I see about Go convinces me they haven't looked at what's already 
out there and they haven't learned from what people have already written and 
they haven't really thought about all the use cases for the features they're 
"reinventing" like this.  Maybe it's great for what google does, but it 
doesn't seem like the general-purpose system language it's hyped as.

-- 
Darren New, San Diego CA, USA (PST)
    C# - a language whose greatest drawback
    is that its best implementation comes
    from a company that doesn't hate Microsoft.

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