file truncate

[Brian T. Rice]

Lendvai Attila wrote:

> and currently the vm generation only works if there is a vm.c/h.
> therefore there's a withNewNamed:do: in the patch, too.

I didn't like this solution (which means I don't like withOpenNamed:do:, 
really), so I cooked up my changes to make File access more Flow-style 
(well, okay, Flow hasn't ever done this, but it seems like what Craig 
Latta would do if he were involved in Slate at all).

What I'm about to commit will make:

Mode objects, to have persistent #open parameters on the File objects 
themselves.
E.g.: File Read, File Write, File ReadWrite, File CreateWrite (all as 
slots on the traits object)

"File newNamed: &mode:" makes a new File object (with a given mode or 
the same as default / first argument), and does NOT open it.

This means that you can grab some File object, and repeatedly call #open 
and #close on it consistently, even across image-saves (which is where 
you want some automation for it anyway).

So, to replace this method, sessionDo: takes an ExternalResource (not 
just a File) and runs:

r@(ExternalResource traits) sessionDo: block
"Calls the block with the resource object as input, opening and closing 
it transparently in an error-tolerant way. The return value of the block 
is answered if it completes without error."
[
   [r open.
    block applyWith: r]
      ensure: [r isOpen ifTrue: [r commit. r close]]
].

This is even simpler than withOpenNamed:do: and avoids the "did the code 
fail creating the object in the first place?" uncertainty. In fact you 
can implement with- with sessionDo:.

Unfortunately, it'll take an image rebuild to incorporate these changes, 
as far as I can tell. At least, this is the case for a lot of code 
critical to the image operation until forwardTo: usage is standardized 
into things like addPrototype:derivedFrom:.

PS: Also, I finally am changing atEnd to isAtEnd, as requested some 
months ago.

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