I can't remember this word that describes common standards and practices in the language that one is programming in. For instance:
in Java:
Putting curly braces on the same line:
public void x() {
}
vs
public void x()
{
}
Is an example of this word I am searching for. It's fairly common in the online community. It's similar to pragmatic, ubiquitous, and common, but it's a bit more fancy. Thanks for your help.
The word I was searching for is idiomatic
Related
From reading this (https://www.educative.io/edpresso/what-is-a-dart-symbol) it seems that Symbols are deprecated in Dart. But I've had trouble finding an explanation for why to avoid them. This answer (Dart symbol literals) gives some explanation of what symbols are in dart, certain cases when they're commonly used. And it suggests "you shouldn't need to use symbols outside of those cases." Shouldn't need is different than shouldn't. Are they deprecated or not? If they are deprecated, why?
The docs here: (https://api.dart.dev/stable/2.12.4/dart-core/Symbol-class.html) don't mention deprecation. I couldn't find any mention of Symbols here: (https://dart.dev/guides/language/effective-dart) either for or against.
In this example the symbol seems to be working as I'd like it to:
class TrafficLight {
Symbol color;
TrafficLight(this.color);
}
void main() {
var t = TrafficLight(#red);
print(t.color == #red);
print(t.color == #green);
}
//returns:
// > true
// > false
If I have thousands of traffic lights, thousands of identical Strings are a waste of RAM. What's the common / best practice way of handling these type of situations in Dart? Enums? Creating a TrafficLightColor class?
Thanks in advance for any light you can shed on this issue.
Response to comments
#julemand101
void main() {
String a = '123';
String b = a;
a += 'foo';
print('a: $a');
print('b: $b');
}
return is:
a: 123foo b: 123
If they were pointing to the same object, I'd expect return to be
a: 123foo b: 123foo
#julemand101, You're absolutely right, my thinking was off. Thanks for the explanation.
Symbols are not deprecated. They are mainly used for reflection-like functionality like dart:mirrors, Object.noSuchMethod (the memberName and namedArguments names) and Function.apply (again the named arguments names). If you don't need those, you likely don't need to bother with symbols. You can, they're just objects, but not particularly useful objects.
(Some libraries use private symbols, like #_foo to create a library-private sentinel object, but you could also just do final _mySentinel = Object();.)
The best way to handle the traffic lights situation is enums.
You could use symbol literals (#red, #green) or string literals ("red", "green") or magic numbers (1, 2), but the only approach to creating a fixed set of values to represent a specific thing that is language and type-system supported is enums.
You can make your own enum-like class if you want to, and it'll be just as good as enums, except that you won't get a warning if you forget a case in a switch.
(If you do use string literals, you'll likely find that they are canonicalized too, so the string data won't take up more space whether they occur once or thousands of times).
With dart it is possible to prefix class/function definition by a commentary so that the analyzer will interpret it as documentation:
/// Some documentation for [Foo]
class Foo {
}
But how can I achieve the same behavior, with parameters instead?
I tried the following:
void myFunction(
/// Some parameter documentation
String parameter,
) {
}
But this doesn't work.
However, it seems possible because dartanalyzer do contain a property on ParameterElement for documentation.
https://www.dartlang.org/guides/language/effective-dart/documentation
Here's the offical Dart language guidelines for documentation best practice. It covers most/all cases and has great examples of do's and don't's.
This bit shows the way to include parameters. Basically, wrap the parameters in square brackets and within a sentence explaining it.
Does Swift provide a native Design by Contract support? I understand that it can be done during runtime through assertions, but could it be done during compile time? Or, are there any external plugins/libraries that do this?
EDIT
By saying "during compile time Design by Contract", I do not mean the library to be an all powerful static analyser that C# has. It would be enough for me if it is something like the one that iContract provides for Java. Let us look at an example:
A DBC code for the square root evaluation in Java using iContract could be written as :
/**
* #pre f >= 0.0
* #post Math.abs((return * return) - f) < 0.001
*/
public float sqrt(float f) { ... }
Now, this keeps my contract as a part of my API specification rather than a part of its implementation which I believe is a cleaner way. The caller will know what his responsibilities are and the callee is setting its expectation, all in albeit clearer manner. Do we have something like this in Swift?
TL;DR
As #Tommy points out in the comments under your question, it would appear that the plain & simple answer to your question is "No, compile time DbC is not currently a feature of Swift".
What's built in right now?
For built-in support for this type of design strategy, you currently have to look at the runtime I'm afraid. Swift appears to prefer runtime assertions for enforcing preconditions currently, although the language seems generally to be putting more emphasis on safety at compile time (more on this below). The global functions assert, assertionFailure, precondition and preconditionFailure are designed to be sprinkled liberally throughout code without impacting release build performance.
Unit tests are, of course, another strategy for checking that API contracts are fulfilled, but these must be thought of and implemented manually, and so are error prone.
Something else that is perhaps interesting to note is that amongst the better documentation comment support of Swift 2, "requires", "precondition" and "postcondition" are recognised markup keywords, such that they are displayed prominently in quick help documentation:
/// - precondition: f >= 0.0
/// - postcondition: abs((return * return) - f) < 0.001
/// - returns: The square root of `f`.
func sqrt(f: Float) -> Float { ... }
So does this emphasis on being able to provide good documentation for API contracts mean that the Swift development team clearly cares about it, and this is a stop-gap until they incorporate something into the syntax in the future, or does it mean that they think this sort of information belongs in the documentation? Pointless postulation, perhaps. Regardless, despite the fact it's not proper DbC, I think it's a handy thing to be aware of right now.
What can I do about it now?
With Objective-C, macros could be used to essentially implement basic DbC, however the lack of macros in Swift means you would have to resort to some kind of function/generics-based wrapper, which I think would look like a really awkward bodge.
Xcode's support for adding custom scripts to a target's build phases – as suggested by #JonShier in the comments – is perhaps the closest you will get to useful & automatic DbC without waiting for the language to (maybe / maybe not) introduce such a feature. With the aforementioned documentation markup keywords, a script that analyses documentation comments to build unit tests could even be incorporated retrospectively to projects with only a small amount of learning/effort on the part of the user. As you say, I think this could make a very interesting project!
Will it be a built-in feature in the future?
It is not clear whether or not native DbC might be incorporated into Swift in the future. Arguably, it is a feature that is well suited to the mission of the Swift language, which is to say that it promotes safer code and reduced risk of runtime errors. Should it become a part of the language, I would suggest that we would be more likely to see them appear as declaration attributes than as interpreted comment markup, for example:
#contract(
precondition = f >= 0.0,
postcondition = abs((return * return) - f) < 0.001
)
func sqrt(f: Float) -> Float { ... }
(But that is just speculation, and of no use to us right now!)
From what I know of the topic, compile-time DbC can be a very complex problem. But who knows... work on the Clang Static Analyzer has certainly shown that there is an underlying desire to drag identification of runtime bugs back to compile time. Perhaps this is the perfect problem to put a Swift static analyser to work on in the future?
I'm not if this is what you're looking for but here is a suggestion you could try maybe.
If you want to define a protocol where you can define the signature of the sqrt function and leave the implementation for other classes or structs to implement at a later point you could do something like the code below:
Note: the the sqrtf is just using the system implementation here.
public protocol Math {
func sqrtf(f: Float) -> Float
}
struct NativeMath: Math {
func sqrtf(f: Float) -> Float {
return sqrt(f)
}
}
println(NativeMath().sqrtf(2))
Could somebody please write some formal definition of keyword with in Dart?
In official Dart examples I have only found:
class TaskElement extends LIElement with Polymer, Observable {
But I still can't understand what is it exactly doing.
The with keyword indicates the use of a "mixin". See here.
A mixin refers to the ability to add the capabilities of another class or classes to your own class, without inheriting from those classes. The methods of those classes can now be called on your class, and the code within those classes will execute. Dart does not have multiple inheritance, but the use of mixins allows you to fold in other classes to achieve code reuse while avoiding the issues that multiple inheritance would cause.
I note that you have answered some questions about Java -- in Java terms, you can think of a mixin as an interface that lets you not merely specify that a given class will contain a given method, but also provide the code for that method.
You can think mixin as Interface in Java and like protocol in Swift.Here is the simple example.
mixin Human {
String name;
int age;
void about();
}
class Doctor with Human {
String specialization;
Doctor(String doctorName, int doctorAge, String specialization) {
name = doctorName;
age = doctorAge;
this.specialization = specialization;
}
void about() {
print('$name is $age years old. He is $specialization specialist.');
}
}
void main() {
Doctor doctor = Doctor("Harish Chandra", 54, 'child');
print(doctor.name);
print(doctor.age);
doctor.about();
}
Hope it help to understand.
What is the proper functional way to handle pluggability in projects? I am working on a new opensource project in F# and can not seem to get the object oriented idea of plugins and interfaces out of my mind. Things I would like to be able to swap out are loggers, datastoring, and authentication.
I have been searching quite a bit for an answer to this and havent come up with much except for this:
http://flyingfrogblog.blogspot.com/2010/12/extensibility-in-functional-programming.html
The answer to this question would be different for different functional languages. F# is not purely functional - it takes the best from functional, imperative and also object-oriented worlds.
For things like logging and authentication, the most pragmatic approach would be to use interfaces (in F#, it is perfectly fine to use interfaces, but people do not generally use inheritance and prefer composition instead).
A simple interface makes sense when you have multiple different functions that you can invoke:
type IAuthentication =
abstract Authenticate : string * string -> bool
abstract ResetPassword : string * string -> void
You can use object expressions, which is a really nice way to implement interfaces in F#.
If you have just a single function (like logging a message), then you can parameterize your code by a function (which is like an interface with just a single method):
type Logger = string -> unit
For things like authentication and logging (that probably do not change while the application is running), you can use a global mutable value. Although if you want to synchronize requests from multiple threads and there is some mutable state, it might be a good idea to write an F# agent.