Rxjava: Support Observable.from(array_of_primitives)

[tomkur]

It seems that it is currently impossible to create an Observable from an array of primitives, e.g.:

char[] chars = "some string".toCharArray();
Observable.from(chars); //does not compile

Is this a conscious decision?

[vanniktech]

Could not you just use Observable.from(Arrays.asList(chars)) ?

[tomkur]

There's a gotcha with this approach. Arrays.asList(chars) will return a one-element list containing char array chars instead of list of characters from chars. So it's not what I'd hope for and I can't use it with Observable the way I'd like to.

I can use third-party library, like Guava and have Chars.asList(chars), but I'd prefer to avoid having such dependency.

[abersnaze]

We named it just.

[akarnokd]

A proper support would require specializing RxJava types to primitive types which is quite cumbersome for minimal benefit.

[tomkur]

I probably didn't make myself clear. I'd like to have an option to observe a sequence of characters in a String, so that:

char[] chars = "some string".toCharArray();
Observable.from(chars).subscribe(curr -> System.out.println("next: " + curr)); //currently does not compile

outputs:

next: s
next: o
next: m
next: e
next:  
next: s
next: t
next: r
next: i
next: n
next: g

The options you mentioned work the following way:

Observable.from(Arrays.asList(chars)).subscribe(curr -> System.out.println("next: " + curr)); 

outputs:

next: [C@6193b845

and the same for the other case

Observable.just(chars).subscribe(curr -> System.out.println("next: " + curr));

outputs:

next: [C@1f17ae12

[akarnokd]

char[] chars = "string".toCharArray();

Observable.range(0, chars.length).map(i -> chars[i]).subscribe(...)

[tomkur]

@akarnokd I can understand it as long as it's a conscious decision. Note however that without this support it's easy to fall for a trap, such as:

Observable.from(Arrays.asList(chars))

which as described above does not do what might seem most intuitive.
In Java typically you'll have many overloads of methods accepting array of primitive types, e.g.

Arrays.copyOf(T[] original, int newLength)
Arrays.copyOf(boolean[] original, int newLength)
Arrays.copyOf(byte[] original, int newLength)
Arrays.copyOf(char[] original, int newLength)
//and others

[tomkur]

@akarnokd regarding your example - sure, it's doable, I'm just asking to facilitate usage.

[akarnokd]

Such source factory methods doesn't have to be on the Observable itself so you can have your own class with from in it. You can take the OnSubscribeFromArray implementation of #3477 and change the array type at your leisure.

[ultraon]

Another way to do it:
Observable.fromArray("string".split("")).map(s -> s.charAt(0)).subscribe(...)