Arg<T>.Property is part of the documentation on inline constraints for Rhino Mocks v3.5, but I can't find it in v.3.6. What happened?
The documentation is here: http://ayende.com/Wiki/Rhino+Mocks+3.5.ashx?AspxAutoDetectCookieSupport=1#SimpleConstraints
and Arg<T>.Property is mentioned in the constraints reference table.
This seems to be a bug in the documentation. When examining the Rhino.Mocks.dll (3.6.0.0) in the Object Browser I see that Rhino.Mocks.Arg<T> only offers the methods Is and List but not Property.
However Rhino.Mocks.Constraints contains the Property class. Using the "old" syntax you should be able to do the same:
AAA syntax (producing compile error):
myStub.Expect(x => x.MethodToCall(Arg<T>.Property.Value("PropertyName", myDesiredPropertyValue))).Result(myMockResult);
Old syntax (working):
myStub.Expect(x => x.MethodToCall(null)).Constraints(Property.Value("PropertyName", myDesiredPropertyValue)).Result(myMockResult);
The documentation says "You're probably used to IgnoreArguments(), Constraints() and RefOut(). [...] It is encouraged to use only Arg<T>, it is more consistent and easier to understand, even if sometimes a little more to write."
As Jeff Bridgman noted, you can also use Arg<T>.Matches:
myStub.Expect(x => x.MethodToCall(Arg<T>.Matches(m => m.PropertyName == myDesiredPropertyValue))).Result(myMockResult);
It has the advantage of being 'refactory safe', meaning that you can refactor the name of the property safely without the need to search for any 'magic strings'. It also meets the suggestion in the documentation to rather use Arg<T> instead of Constraints().
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.
I’m trying to figure out what the differences are between the above-mentioned routines, and if statements like
say $y.Bool;
say $y.so;
say ? $y;
say so $y;
would ever produce a different result.
So far the only difference that is apparent to me is that ? has a higher precedence than so. .Bool and .so seem to be completely synonymous. Is that correct and (practically speaking) the full story?
What I've done to answer your question is to spelunk the Rakudo compiler source code.
As you note, one aspect that differs between the prefixes is parsing differences. The variations have different precedences and so is alphabetic whereas ? is punctuation. To see the precise code controlling this parsing, view Rakudo's Grammar.nqp and search within that page for prefix:sym<...> where the ... is ?, so, etc. It looks like ternary (... ?? ... !! ...) turns into an if. I see that none of these tokens have correspondingly named Actions.pm6 methods. As a somewhat wild guess perhaps the code generation that corresponds to them is handled by this part of method EXPR. (Anyone know, or care to follow the instructions in this blog post to find out?)
The definitions in Bool.pm6 and Mu.pm6 show that:
In Mu.pm6 the method .Bool returns False for an undefined object and .defined otherwise. In turn .defined returns False for an undefined object and True otherwise. So these are the default.
.defined is documented as overridden in two built in classes and .Bool in 19.
so, .so, and ? all call the same code that defers to Bool / .Bool. In theory classes/modules could override these instead of, or as well, as overriding .Bool or .defined, but I can't see why anyone would ever do that either in the built in classes/modules or userland ones.
not and ! are the same (except that use of ! with :exists dies) and both turn into calls to nqp::hllbool(nqp::not_i(nqp::istrue(...))). I presume the primary reason they don't go through the usual .Bool route is to avoid marking handling of Failures.
There are .so and .not methods defined in Mu.pm6. They just call .Bool.
There are boolean bitwise operators that include a ?. They are far adrift from your question but their code is included in the links above.
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.
What happened to me while programming in Java:
String str
// want to call something(), but signature does not match
something(Foo foo)
// but I have this conversion function
Foo fooFrom(String)
// Obviously I am about to create another method overload.. sigh
something(String s) {
something(fooFrom(s));
}
But then I thought of the possibility of a "automatic type conversion" which just uses my defined conversion function fooFrom everytime a string is passed in where a Foo object is excepted.
My search brought me to the wikipedia page about type conversion with this Eiffel example:
class STRING_8
…
create
make_from_cil
…
convert
make_from_cil ({SYSTEM_STRING})
to_cil: {SYSTEM_STRING}
…
The methods after convert are called automatically if a STRING_8 is used as a SYSTEM_STRING and vice-versa.
Somehow surprising for me I could not find any other language supporting this.
So my question: are there any other languages supporting this feature?
If not, are there any reasons for that, since it seems quite useful to me?
Further I think it would not be difficult to implement it as a language add-on.
There is one minor point that may make the things a bit more complicated. At the moment Eiffel has a rule that conversion can be applied only when the source of reattachment is attached to an object, i.e. is not Void (not null in Java/C#).
Let's look at the original example:
something (str);
Suppose that str is null. Do we get a NullPointerException / InvalidArgumentException, because the code is transformed into
something (fooFrom (str));
and fooFrom does not expect null? Or is the compiler smart enough to transform this into
if (str == null)
something (null);
else
something (fooFrom (str));
?
The current Eiffel standard makes sure that such issues simply do not happen and str is not null if conversion is involved. However many other languages like Java or C# do not guarantee that and the additional complexity may be not worth the effort for them.
I believe that Eiffel is not the only language to support conversion routines, but I would say that it might be one of the very few that integrate this very nicely with the rest of the language definition.
In .NET, for example, you have both op_Explicit and op_Implicit routines that can be used for conversion for languages that support them. And I believe C# does.
Manu
Type coercion (implicit conversion) is a curse and a blessing--handy in some case, but it can also backfire.
For instance, Javascript has many weird coercion rules, that can leads to bug when coercings string to number, etc.
Scala has something called "implicit" which achieves something similar (at least to me) to what you describe in Eiffel. With little surprise, they can lead to certain gotchas. But they can be also very handy, see for instance the article Pimp My Library.
C++ has copy constructors and assignment operator.
I've seen this opportunity reported at least half a dozen times with about as many responses.
My problem is, I've got a MySQL database function defined, we'll call it "my_func(int val) returns int", which works fine if I test directly on the database.
I've also gotten it to work with a direct SQL passthrough my repository implementation, which is okay, but I'd rather route it through Hql, for some god-awful reason...
So... I've got a MySQL5Dialect setup to register the function and I'm having some difficulty parsing through the expected conventions.
My understanding is that I need to prefix the function name with "dbo." at some point during the function registration?
Something like this,
//...
RegisterFunction("my_func", new SQLFunctionTemplate(NHibernateUtil.Int32, "my_func(?1)"));
//...
And then through my repository,
var value = repository.FindByHQL<int>("select my_func(2)").Single();
Where FindByHQL returns an IList.
Any thoughts why this wouldn't work.
I'm running the latest WAMP (2.1e I think).
Enough info? Let me know if I can provide any further details.
Thanks,
Michael
select my_func(2)
is not valid HQL, regardless of whether the function is registered or not.
You can use SQL instead if that's your use case.
Post full exception with stack trace if it's not and this was just a simplified example.