I'm writing code using Twisted, and having trouble coming up with a sensible variable name for my twisted internet deferred's. Here are my candidates:
d : Too generic, too short, violates pylint rule C0103.
def : Conflicts with function defintion builtin.
defer : Conflicts with module twisted.internet.defer
deferred : OK but pretty long
cb : Still too short, violates pylint C0103, conflicts with many callback method names.
cback : Too Weird?
callback : Conflicts with method Deferred.callback()
I'm looking for other suggestions. It seems like most of the Twisted example code uses "d" which is fine for simple invocations, but when you're passing Deferred's around to methods and storing them as member variables, it's really far too descriptive.
It's good to name the Deferred meaningfully - as of course you would name any variable.
A good thing to name it after is the event that its firing signals.
Some examples:
pageGotten = getPage('http://...')
whenAuthenticated = client.authenticate(...)
taskDone = doTask(...)
Related
Example:
data class T(val flag: Boolean) {
constructor(n: Int) : this(run {
// Some computation here...
<Boolean result>
})
}
In this example, the custom constructor needs to run some computation in order to determine which value to pass to the primary constructor, but the compiler does not accept the run, citing Cannot access 'run' before superclass constructor has been called, which, if I understand correctly, means instead of interpreting it as the non-extension run (the variant with no object reference in https://kotlinlang.org/docs/reference/scope-functions.html#function-selection), it construes it as a call to this.run (the variant with an object reference in the above table) - which is invalid as the object has not completely instantiated yet.
What can I do in order to let the compiler know I mean the run function which is not an extension method and doesn't take a scope?
Clarification: I am interested in an answer to the question as asked, not in a workaround.
I can think of several workarounds - ways to rewrite this code in a way that works as intended without calling run: extracting the code to a function; rewriting it as a (possibly highly nested) let expression; removing the run and invoking the lambda (with () after it) instead (funnily enough, IntelliJ IDEA tags that as Redundant lambda creation and suggests to Inline the body, which reinstates the non-compiling run). But the question is not how to rewrite this without using run - it's how to make run work in this context.
A good answer should do one of the following things:
Explain how to instruct the compiler to call a function rather than an extension method when a name is overloaded, in general; or
Explain how to do that specifically for run; or
Explain that (and ideally also why) it is not possible to do (ideally with supporting references); or
Explain what I got wrong, in case I got something wrong and the whole question is irrelevant (e.g. if my analysis is incorrect, and the problem is something other than the compiler construing the call to run as this.run).
If someone has a neat workaround not mentioned above they're welcome to post it in a comment - not as an answer.
In case it matters: I'm using multi-platform Kotlin 1.4.20.
Kotlin favors the receiver overload if it is in scope. The solution is to use the fully qualified name of the non-receiver function:
kotlin.run { //...
The specification is explained here.
Another option when the overloads are not in the same package is to use import renaming, but that won't work in this case since both run functions are in the same package.
Given the documentation and the comments on an earlier question, by request I've made a minimal reproducible example that demonstrates a difference between these two statements:
my %*SUB-MAIN-OPTS = :named-anywhere;
PROCESS::<%SUB-MAIN-OPTS><named-anywhere> = True;
Given a script file with only this:
#!/usr/bin/env raku
use MyApp::Tools::CLI;
and a module file in MyApp/Tools called CLI.pm6:
#PROCESS::<%SUB-MAIN-OPTS><named-anywhere> = True;
my %*SUB-MAIN-OPTS = :named-anywhere;
proto MAIN(|) is export {*}
multi MAIN( 'add', :h( :$hostnames ) ) {
for #$hostnames -> $host {
say $host;
}
}
multi MAIN( 'remove', *#hostnames ) {
for #hostnames -> $host {
say $host;
}
}
The following invocation from the command line will not result in a recognized subroutine, but show the usage:
mre.raku add -h=localhost -h=test1
Switching my %*SUB-MAIN-OPTS = :named-anywhere; for PROCESS::<%SUB-MAIN-OPTS><named-anywhere> = True; will print two lines with the two hostnames provided, as expected.
If however, this is done in a single file as below, both work identical:
#!/usr/bin/env raku
#PROCESS::<%SUB-MAIN-OPTS><named-anywhere> = True;
my %*SUB-MAIN-OPTS = :named-anywhere;
proto MAIN(|) is export {*}
multi MAIN( 'add', :h( :$hostnames )) {
for #$hostnames -> $host {
say $host;
}
}
multi MAIN( 'remove', *#hostnames ) {
for #hostnames -> $host {
say $host;
}
}
I find this hard to understand.
When reproducing this, be alert of how each command must be called.
mre.raku remove localhost test1
mre.raku add -h=localhost -h=test1
So a named array-reference is not recognized when this is used in a separate file with my %*SUB-MAIN-OPTS = :named-anywhere;. While PROCESS::<%SUB-MAIN-OPTS><named-anywhere> = True; always works. And for a slurpy array, both work identical in both cases.
The problem is that it isn't the same variable in both the script and in the module.
Sure they have the same name, but that doesn't mean much.
my \A = anon class Foo {}
my \B = anon class Foo {}
A ~~ B; # False
B ~~ A; # False
A === B; # False
Those two classes have the same name, but are separate entities.
If you look at the code for other built-in dynamic variables, you see something like:
Rakudo::Internals.REGISTER-DYNAMIC: '$*EXECUTABLE-NAME', {
PROCESS::<$EXECUTABLE-NAME> := $*EXECUTABLE.basename;
}
This makes sure that the variable is installed into the right place so that it works for every compilation unit.
If you look for %*SUB-MAIN-OPTS, the only thing you find is this line:
my %sub-main-opts := %*SUB-MAIN-OPTS // {};
That looks for the variable in the main compilation unit. If it isn't found it creates and uses an empty Hash.
So when you try do it in a scope other than the main compilation unit, it isn't in a place where it could be found by that line.
To test if adding that fixes the issue, you can add this to the top of the main compilation unit. (The script that loads the module.)
BEGIN Rakudo::Internals.REGISTER-DYNAMIC: '%*SUB-MAIN-OPTS', {
PROCESS::<%SUB-MAIN-OPTS> := {}
}
Then in the module, write this:
%*SUB-MAIN-OPTS = :named-anywhere;
Or better yet this:
%*SUB-MAIN-OPTS<named-anywhere> = True;
After trying this, it seems to work just fine.
The thing is, that something like that used to be there.
It was removed on the thought that it slows down every Raku program.
Though I think that any slowdown it caused would still be an issue as the line that is still there has to look to see if there is a dynamic variable of that name.
(There are more reasons given, and I frankly disagree with all of them.)
May a cuppa bring enlightenment to future SO readers pondering the meaning of things.[1]
Related answers by Liz
I think Liz's answer to an SO asking a similar question may be a good read for a basic explanation of why a my (which is like a lesser our) in the mainline of a module doesn't work, or at least confirmation that core devs know about it.
Her later answer to another SO explains how one can use my by putting it inside a RUN-MAIN.
Why does a slurpy array work by default but not named anywhere?
One rich resource on why things are the way they are is the section Declaring a MAIN subroutine of S06 (Synopsis on Subroutines)[2].
A key excerpt:
As usual, switches are assumed to be first, and everything after the first non-switch, or any switches after a --, are treated as positionals or go into the slurpy array (even if they look like switches).
So it looks like this is where the default behavior, in which nameds can't go anywhere, comes from; it seems that #Larry[3] was claiming that the "usual" shell convention was as described, and implicitly arguing that this should dictate that the default behavior was as it is.
Since Raku was officially released RFC: Allow subcommands in MAIN put us on the path to todays' :named-anywhere option. The RFC presented a very powerful 1-2 punch -- an unimpeachable two line hackers' prose/data argument that quickly led to rough consensus, with a working code PR with this commit message:
Allow --named-switches anywhere in command line.
Raku was GNU-like in that it has '--double-dashes' and that it stops interpreting named parameters when it encounters '--', but unlike GNU-like parsing, it also stopped interpreting named parameters when encountering any positional argument. This patch makes it a bit more GNU-like by allowing named arguments after a positional, to prepare for allowing subcommands.
> Alter how arguments are processed before they're passed to sub MAIN
In the above linked section of S06 #Larry also wrote:
Ordinarily a top-level Raku "script" just evaluates its anonymous mainline code and exits. During the mainline code, the program's arguments are available in raw form from the #*ARGS array.
The point here being that you can preprocess #*ARGS before they're passed to MAIN.
Continuing:
At the end of the mainline code, however, a MAIN subroutine will be called with whatever command-line arguments remain in #*ARGS.
Note that, as explained by Liz, Raku now has a RUN-MAIN routine that's called prior to calling MAIN.
Then comes the standard argument processing (alterable by using standard options, of which there's currently only the :named-anywhere one, or userland modules such as SuperMAIN which add in various other features).
And finally #Larry notes that:
Other [command line parsing] policies may easily be introduced by calling MAIN explicitly. For instance, you can parse your arguments with a grammar and pass the resulting Match object as a Capture to MAIN.
A doc fix?
Yesterday you wrote a comment suggesting a doc fix.
I now see that we (collectively) know about the coding issue. So why is the doc as it is? I think the combination of your SO and the prior ones provide enough anecdata to support at least considering filing a doc issue to the contrary. Then again Liz hints in one of the SO's that a fix might be coming, at least for ours. And SO is itself arguably doc. So maybe it's better to wait? I'll punt and let you decide. At least you now have several SOs to quote if you decide to file a doc issue.
Footnotes
[1] I want to be clear that if anyone perceives any fault associated with posting this SO then they're right, and the fault is entirely mine. I mentioned to #acw that I'd already done a search so they could quite reasonably have concluded there was no point in them doing one as well. So, mea culpa, bad coffee inspired puns included. (Bad puns, not bad coffee.)
[2] Imo these old historical speculative design docs are worth reading and rereading as you get to know Raku, despite them being obsolete in parts.
[3] #Larry emerged in Raku culture as a fun and convenient shorthand for Larry Wall et al, the Raku language team led by Larry.
From the docs that say,
Returns the self-reference to the instance itself:
my $b; # defaults to Any
say $b.serial.^name; # OUTPUT: «Any»
my $breakfast = 'food';
$breakfast.serial.say; # OUTPUT: «food»
I do not have the foggiest what this routine does, please can someone explain?
On Supplys, it is an informational method that is supposed to indicate whether there will never be any concurrent emit on that Supply.
On HyperSeq and RaceSeq, it returns a serialized Seq, so you could consider it the opposite of the hyper and race method.
In general, it appears to return itself, which seems to make sense from the HyperSeq and RaceSeq point of view.
And yes, these should be documented properly, so please create a documentation issue. Thank you!
In the doc example it does nothing. That is, if you remove it you get the same results:
my $b; # defaults to Any
say $b.^name; # OUTPUT: «Any»
my $breakfast = 'food';
$breakfast.say; # OUTPUT: «food»
More generally, I think you'd best ignore the serial method other than to open a doc issue pointing to this SO if you'd like to improve the doc.
The serial method does not appear to be in the official language
A search of the roast repo for "serial" yields zero matches.
Within Rakudo source code the method name serial has been overloaded to have one of three meanings:
A boolean declaring whether a Supply sequence is always serial. Rakudo source examples: 1, 2. This looks to me like an internal method that doesn't need to be documented.
A coercion of parallel sequence (hyper or race) to a serial version of the same sequence. This looks to me like an internal method that doesn't need to be documented.
A "no op" that returns its invocant. I suspect it would be best if it were not documented, at least until such time as its raison d'etre is clear; its official status viz-a-viz the spec (roast) is clear; and/or there's an attempt to systematically document which operations have the is nodal set on them.
None of the above seems to warrant ordinary users' attention or documentation.
The Any class definition of a serial method seems pointless
The Any class serial method returns self, i.e. when called it is a no op.
I don't currently understand why there is an Any class definition.
One possible point for it would be that there are .serial calls made by internal code on instances of an unknown and generally unknowable class and there thus needs to be a default definition of serial in the Any class.
But a search of the rakudo repo for ".serial" suggests that calls are only made to supplies or hyper/race seqs.
That said, I note the is nodal trait on the proto serial declaration in Any that immediately precedes the multi method serial declaration. Perhaps that is the reason it's in Any.
See also Arbitrary drift of methods to Mu and Any.
The documentation you quoted seems pointless
The definition and example seem to reflect someone's sense of humor. I applaud use of humor but in this case I suspect the best improvement would be to just remove the page you linked.
The title pretty much sums it up, but here's the long version anyway.
After posting a small snippet of perl code, I was told to avoid indirect object notation, "as it has several side effects". The comment referenced this particular line:
my $some_object = new Some::Module(FIELD => 'value');
As this is how I've always done it, in an effort to get with the times I therefore ask:
What's so bad about it? (specifically)
What are the potential (presumably negative) side effects?
How should that line be rewritten?
I was about to ask the commenter, but to me this is worthy of its own post.
The main problem is that it's ambiguous. Does
my $some_object = new Some::Module(FIELD => 'value');
mean to call the new method in the Some::Module package, or does it mean to call the new function in the current package with the result of calling the Module function in the Some package with the given parameters?
i.e, it could be parsed as:
# method call
my $some_object = Some::Module->new(FIELD => 'value');
# or function call
my $some_object = new(Some::Module(FIELD => 'value'));
The alternative is to use the explicit method call notation Some::Module->new(...).
Normally, the parser guesses correctly, but the best practice is to avoid the ambiguity.
What's so bad about it?
The problems with Indirect Method Notation are avoidable, but it's far easier to tell people to avoid Indirect Method Notation.
The main problem it's very easy to call the wrong function by accident. Take the following code, for example:
package Widget;
sub new { ... }
sub foo { ... }
sub bar { ... }
sub method {
...;
my $o = new SubWidget;
...;
}
1;
In that code, new SubWidget is expected to mean
SubWidget->new()
Instead, it actually means
new("SubWidget")
That said, using strict will catch most of these instances of this error. Were use strict; to be added to the above snippet, the following error would be produced:
Bareword "SubWidget" not allowed while "strict subs" in use at Widget.pm line 11.
That said, there are cases where using strict would not catch the error. They primarily involve the use of parens around the arguments of the method call (e.g. new SubWidget($x)).
So that means
Using Indirect Object Notation without parens can result in odd error messages.
Using Indirect Object Notation with parens can result in the wrong code being called.
The former is bearable, and the latter is avoidable. But rather than telling people "avoid using parens around the arguments of method calls using Indirect Method Notation", we simply tell people "avoid using Indirect Method Notation". It's just too fragile.
There's another issue. It's not just using Indirect Object Notation that's a problem, it's supporting it in Perl. The existence of the feature causes multiple problems. Primarily,
It causes some syntax errors to result in very odd/misleading error messages because the code appeared to be using ION when it wasn't.
It prevents useful features from being implemented since they clash with valid ION syntax.
On the plus side, using no indirect; helps the first problem.
How should that line be rewritten?
The correct way to write the method call is the following:
my $some_object = Some::Module->new(FIELD => 'value');
That said, even this syntax is ambiguous. It will first check if a function named Some::Module exists. But that's so very unlikely that very few people protect themselves from such problems. If you wanted to protect yourself, you could use the following:
my $some_object = Some::Module::->new(FIELD => 'value');
As to how to avoid it: There's a CPAN module that forbids the notation, acting like a pragma module:
no indirect;
http://metacpan.org/pod/indirect
The commenter just wanted to see Some::Module->new(FIELD => 'value'); as the constructor.
Perl can use indirect object syntax for other bare words that look like they might be methods, but nowadays the perlobj documentation suggests not to use it.
The general problem with it is that code written this way is ambiguous and exercises Perl's parser to test the namespace to e.g. check when you write method Namespace whether Namespace::method exists.
I have a class and I want to change the name of a specific method in run time.
I guess there's a method in the 'Behavior' class that does it. But I just can't find it. any help? [in squeak]
The normal way a user does this is to modify the method source and 'accept it' then delete the old version. So it's not likely that basic Squeak includes a single method to do this, although I could be wrong.
However if you install, for example, OmniBrowser there is a method refactoring called 'rename' and you could inspect and find code to perform this refactoring. It is fairly complex, firstly because the refactorings are done using the command pattern which involves a little redirection to work out, but secondly because this is a fairly complex refactoring which includes modifying the call sites.
What you are suggesting puts HUGE red flags up for me.
What is it you are trying to accomplish with this?
Do you mean you want to change the name of the method you are calling at runtime?
If so, that's easy.
do something like:
|methodName|
methodName := self useMethod1 ifTrue: [#method1 ] ifFalse:[ #method2 ].
self perform: methodName.
You best use a refactoring
r := RenameMethodRefactoring
renameMethod: #foo:foo:
in: Foo
to: #bar:bar:
permutation: (1 to: #foo:foo: numArgs).
r execute.
Avoid voodoo magic in real code when possible.
That being said you can do some very interesting things by manipulating methods dynamically.
For instance the code bricks in Etoys are translated into Smalltalk methods. Other DSL implementations can also benefit from similar metaprogramming tricks.
After experimenting a bit I came up with the following code for renaming unary methods:
renameMethod: oldMethod inClass: class to: newMethod
| oldSelector newSelector source parser |
oldSelector := oldMethod asSymbol.
newSelector := newMethod asSymbol.
oldSelector = newSelector ifTrue: [^self].
"Get method category"
category := (LocatedMethod location: class selector: oldSelector) category.
"Get method source code"
source := class sourceCodeAt: oldSelector.
"Replace selector in method source"
(parser := class parserClass new) parseSelector: source.
source := (newSelector asString), (source allButFirst: parser endOfLastToken).
"Compile modified source"
class compile: source classified: category.
"Remove old selector"
class removeSelector: oldSelector
You could probably find an easier way to do this if you browse through the Squeak code a bit longer than I did.
You can't change a method's name, really, because it doesn't have one.
An object's method dictionary maps Symbols to CompiledMethods. "Change the name of a method" means "move the CompiledMethod value from this key to that key".