On 8/2/2018 1:24 PM, 'John Clements' via Racket Users wrote:
I hate to turn a little question into a big one, but… are parameters the right
choice, here? It seems to me that optional parameters would be more suitable.
Unfortunately, I’ve been on the other side of this fence, too: parameters are
vastly more convenient for implementors than adding optional parameters to
every one of the internal calls. This certainly came up for me in the
construction of a CSV writing library.
I can imagine a bunch of programming patterns that might assist this; the most
obvious one would be an object-like metaphor where parameter values are
represented as an object to which calls are made. Do others have ideas on a
“best practice” for this situation and others like it?
John
In the case in question, I probably would go the object route as well.
Personally, I don't find a lot of use for parameters: my biggest need
for them is in threaded web server code where there may be multiple
instances of a given handler and they need unique identifiers for client
messages, log entries, etc. Generic logging code doesn't know what
thread it's running under, and Racket threads don't have a printable
identifier themselves ... so I parameterize each handler thread with a
useful [to me] identifier.
But parameters aren't useful for sideways communication between
threads. Almost all my use of continuations is for abort / escape
purposes, and I don't find a lot of need there for the "special var"
stack behavior of parameters. For most code where I might possibly use
parameters, I find they just don't add anything over using "global"
variables.
[I put "global" in quotes to mean only "accessible to all the code that
needs and/or shares the variable" - not necessarily that it is defined
at the top level or exported from its module. Even within modules, not
infrequently I use the idiom of defining multiple functions within a let
that defines their shared state. Generally I prefer to limit an
object's visibility to only that code that needs to see it.]
But I imagine there are other people who find parameters invaluable in
their work. Their utility for file I/O using standard ports is obvious
... I just don't tend to write a lot of that kind of code.
YMMV.
George
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