That's true, but if the assignment is explicit (a variable is named, in addition to accessor information), the code can be transparent. Such forms are useful and are used extensively in Common Lisp.
AFAIK Julia lacks symbol macros, so the AST needs to be walked for symbols which satisfy a certain pattern -- the problem is that these macros can have weird corner cases. Best, Tamas On Thu, May 21 2015, David Anthoff <[email protected]> wrote: > I was never a fan of `with`. It makes it really hard to read/reason about > unfamiliar code because you need to know exactly what members a type has in > order to understand what is going on. > > > > From: [email protected] [mailto:[email protected]] On > Behalf Of Stefan Karpinski > Sent: Thursday, May 21, 2015 9:22 AM > To: Julia Users > Subject: Re: [julia-users] Has anyone done a Pascal-style "with" statement > (i.e., macro)? > > > > This seems hard to make sane in a dynamic language. The issue is that `foo` > doesn't give you enough information at compile time to decide which names are > fields of `foo` and which are just local variables. If the first argument to > the @with macro had to be a name of a type – i.e. Foo rather than foo – then > you could do it. You could loosen that up to allow any expression that can be > evaluated at compile time in the global scope where the @with occurs, but > that seems pretty confusing. For example, you couldn't write `@with > typeof(foo)` which is pretty much the first thing that people will try to do. > > > > On Thu, May 21, 2015 at 9:13 AM, Magnus Lie Hetland <[email protected] > <mailto:[email protected]> > wrote: > > A couple of decades ago, I remember using the with statement in Pascal. I > have since wished for it in several languages, but I guess in Julia, it would > probably be feasible without altering the language? > > > > Basically, it'd be something like > > > > type Foo > a > end > > foo = Foo(42) > > @with foo do > a = 1 > b = "frozzbozz" > # ... > end > > # foo.a is now 1 > > That is, let the fields of a composite type be available (syntactically) as > local variables. > > Now, hacking together something like this wouldn't be hard – but making it > really work (without weirdness or performance degradation) seems harder. And > maybe it's a bad idea to begin with. Or maybe someone has already done it?-) > > > > > >
