After browsing through Rescript's API, it seems like there is no function that compares 2 strings that returns a boolean. The best option is localeCompare but it behaves somewhat different from the JS's ==. Why does localeCompare return a float instead of an integer?
You can compare strings using == in rescript as well. Alternatively there is a String.equal as well if you need a function restricted to strings specifically, The "native" (non-Js) standard library modules such as String unfortunately seems to be left out of the rescript documentation entirely.
localeComapre probably returns a float because it might be possible for it to return non-integer numbers. JavaScript unfortunately has no integer type, which makes it hard to know if it could return floats even if it seems obvious that it shouldn't. I've seen several of this kind of bugs myself in various bindings.
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I feel like using operators overloading adds unnecessary complexity and ambiguity to the code.
Does it have its benefits in real-world cases where it's worth to use custom operators or overload existing operators instead of using functions or object methods?
Is it used on a regular basis or more just a funny exotic stuff to add a language a bit more hipness?
The main reason for overloading is comfort of using custom class with mathematic or logic background
like:
vectors
matrices
complex numbers
phasors,tensors,quaternions,...
finite fields
big-numbers (arbnum,biginteger,bigdecimal...)
custom precision floating and fixed formats
predicates,boolean,fuzy and probabilistic
strings,lists,ques
and much much more
If coded right you can write math equations directly and not bother to convert to set of function calls. The reading and understanding math code is much simpler and straightforward with operators.
Sometimes even non strictly math classes are used this way for example images or signals. In DIP/CV there are usually math/physics equations applied on those and overloaded operators make that more simple.
For the non-math classes
are operators usually useless/meaningless (as you feel) except for special operator= which is crucial for any class/struct with dynamic allocation members. Without it things like std:vector<> will not work properly.
Another example are comparison operators which are sometimes implemented for non math classes to make sorting easier.
from wiki
operator overloading—less commonly known as operator ad hoc polymorphism—is a specific case of polymorphism, where different operators have different implementations depending on their arguments
Swift has over 40 operators, all of them are overloaded and we are using them on regular bases. Do you prefer let sum = value.plus(anotherValue) over let sum = value + anotherValue ?? I am sure, you don't! If the value is custom type conforming to protocol Equatable, == operator must be overloaded and we do it regularly.
Is it a good idea to use custom defined operators (like ±, <*> etc ...)? In that area I am not sure. I am not big fan of this ...
Is it a good idea to overload + operator for something else than sum ? No, definitely not!
I've researched this in Swift and am confused on where custom subscripts are useful compared to methods and functions. What is the power in using them rather than using a method/func?
It's purely stylistic. Use a subscript whenever you'd prefer this syntax:
myObject[mySubscript] = newValue
over this one:
myObject.setValue(newValue, forSubscript: mySubscript)
Subscripts are more concise and, when used in appropriate situations, clearer in intent.
Which is an easier, clearer way to refer to an array element: myArray[1] or myArray.objectAtIndex(1)?
Would you like to saymyArray[1...3], or would it by just fine if you had to say something like myArray.sliceFromIndex(1).throughIndex(3) every time?
And hey, you know what? Arithmetic operators are also just functions. So don't we abandon them, so we'd have to say something like
let sum = a.addedTo(b.multipliedBy(c))
Wouldn't that be just the same really? What's the power in having arithmetic operators really?
In C#, the only indexer that actually returns a variable1,2 are array indexers.
void Make42(ref int x) {x=42;}
void SetArray(int[] array){
Make42(ref array[0]);} //works as intended; array[0] becomes 42
void SetList(List<int> list){
Make42(ref list[0]);} //does not work as intended, list[0] stays 0
In the example above, array[0] is a variable, but list[0] is not. This is the culprit behind many developers, writing high-performance libraries, being forced to write their own List implementations (that, unlike the built-in List, expose the underlying array) to get benchmark worthy performance out of the language.
In Swift, ref is called inout and indexer seems to be called subscript. I'm wondering if there's any mechanisms in Swift's subscript to explicitly return a variable rather than a value (a value can be a value-type or reference-type).
If I may bring in C++ parlance, you'd be looking to return a reference to a value. I'm using the term here because it's generally better understood by the programming crowd.
The reason C# limits it to just arrays is that returning arbitrary references may compromise the language's safety guarantees if not done properly.
There appears to be no syntax to return a reference in Swift. Since returning references is hard to verify, and since Swift is rather new and since it aims at being a safe language, it is understandable that Apple didn't go this way.
If you get to a level where you need this kind of performance, you may want to consider C++, in which you can sacrifice almost all the safety you want to get performance.
What is the difference between = and := in Scala?
I have googled extensively for "scala colon-equals", but was unable to find anything definitive.
= in scala is the actual assignment operator -- it does a handful of specific things that for the most part you don't have control over, such as
Giving a val or var a value when it's created
Changing the value of a var
Changing the value of a field on a class
Making a type alias
Probably others
:= is not a built-in operator -- anyone can overload it and define it to mean whatever they like. The reason people like to use := is because it looks very assignmenty and is used as an assignment operator in other languages.
So, if you're trying to find out what := means in the particular library you're using... my advice is look through the Scaladocs (if they exist) for a method named :=.
from Martin Odersky:
Initially we had colon-equals for assignment—just as in Pascal, Modula, and Ada—and a single equals sign for equality. A lot of programming theorists would argue that that's the right way to do it. Assignment is not equality, and you should therefore use a different symbol for assignment. But then I tried it out with some people coming from Java. The reaction I got was, "Well, this looks like an interesting language. But why do you write colon-equals? What is it?" And I explained that its like that in Pascal. They said, "Now I understand, but I don't understand why you insist on doing that." Then I realized this is not something we wanted to insist on. We didn't want to say, "We have a better language because we write colon-equals instead of equals for assignment." It's a totally minor point, and people can get used to either approach. So we decided to not fight convention in these minor things, when there were other places where we did want to make a difference.
from The Goals of Scala's Design
= performs assignment. := is not defined in the standard library or the language specification. It's a name that is free for other libraries or your code to use, if you wish.
Scala allows for operator overloading, where you can define the behaviour of an operator just like you could write a method.
As in other languages, = is an assignment operator.
The is no standard operator I'm aware of called :=, but could define one with this name. If you see an operator like this, you should check up the documentation of whatever you're looking at, or search for where that operator is defined.
There is a lot you can do with Scala operators. You can essentially make an operator out of virtually any characters you like.
Suppose I wish to have 2 functions, one that generates a random integer within a given range, and one that generates a random double within a given range.
int GetRandomNumber( int min, int max );
double GetRandomNumber( double min, double max );
Notice that the method names are the same. I'm trying to decide whether to name the functions that or...
int GetRandomInteger( int min, int max );
double GetRandomDouble( double min, double max );
The first option has the benefit of the user not having to worry about which one they are calling. They can just call GetRandomNumber with integers or doubles and get a result.
The second option is more explicit in the names, but it reveals unneeded information to the caller.
I know this is petty, but I care about petty things.
Edit: How would C++ behave regarding implicit conversion.
Example:
GetRandomNumber( 1, 1 );
This could be implicitly converted for the GetRandomNumber function for the double version. Obviously I don't want this to occur. Will C++ use the int version before the double version?
I prefer your second example, it is explicit and leaves no ambiguity in interpretation. It is better to err on the side of being explicit in method names to clearly illuminate the purpose and function of that member.
The only downside to your approach is that you have coupled the name of the method to the return type which is not ideal in the event that you want to change the return type of one of these methods. However in that case I would be better to add a new method and not break compatibility in your API anyways.
I prefer the second version. I like overloading a function when ultimately the two functions do the same thing; in this case they return different types so they're not quite the same thing. Another possibility if your language supports it is to define it as a generic/template method, like:
T GetRandom<T>(T min, T max);
A function name should tell what the function does; I do not see a point in cramming the types into the names. So definitely go for overloading - that's what it is for.
I prefer the overloaded method. Look at the Math.Min() method in .NET. It has 11 overloads: int, double, byte, etc.
I usually prefer the first example because it doesn't pollute the namespace. For example when calling it, if I pass ints, I'm expecting to get back an int. If I pass in doubles, I probably expect to get back a double. The compiler will give you an error if you write:
//this causes an error
double d = GetRandomNumber(1,10);
so it's not really a big issue. and you can always cast the arguments if you need an int but have doubles for input...
In some of languages you can not vary the return type of overloaded functions this would require the second example.
Assuming C++, the second also avoids problems with ambiguity. If you said:
GetRandomNumber( 1, 5.0 );
which one should be used? In fact, it is a compilation error.
I think the ideal solution would be
Int32.GetRandom(int min, int max)
Double.GetRandom(double min, double max)
but, alas, static extension method are not possible (yet?).
The .net Framwork seems to favor the first option (System.Math class):
public static decimal Abs(decimal value)
public static int Abs(int value)
Like Andrew, I would personally favor the second option to avoid ambiguity, although I do think this is a matter of taste.