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kotlinlang

Hello, World! Isn't there a version of `String.map` fun that returns a String (instead of the generic one returning a List&lt;R&gt;) somewhere?

I guess I can use `.toCharArray().concatToString()`... :slightly_smiling_face:

`somestring.let { s -&gt; someOtherstring }`? return whatever you want from let, it could also be the same data

I think you could make something work with fold actually

you can just do .map.joinToString can't you

actually joinToSTring already takes a transforming function

```    "hello".toList().joinToString { it.toUpperCase() }```


I'm actually not sure why the toList is necessary

because `joinToString()` is defined on Iterable rather than String or CharSequence

Yeah, just realized, the map on CharSequence is a separate thing

this obviously begs the question why CharSequence is its own thing or at least why does CharSequence not at least inherit from Iterable&lt;Char&gt;

My past experience is that every time I see something like this that makes no sense the answer is "because Java" so I'll assume that this is the reason here

ding ding ding: <https://discuss.kotlinlang.org/t/why-doesnt-charsequence-implement-iterable/2485>

sorry I wasn't very clear!

My need was to map chars inside a String to other chars (my specific case: making a String suitable for a file name, so each illegal character is replaced with a space.)

I ended up doing this:
```fun String.asValidFatFileName(): String = map { if (it.isValidFatFileNameChar()) it else ' ' }.toCharArray().concatToString()```
but originally I was a bit surprised that
```fun String.asValidFatFileName(): String = map { if (it.isValidFatFileNameChar()) it else ' ' }```
wasn't enough

yeah, the string API is IMHO hugely confusing

.filter returns a string but .map returns a List&lt;Char&gt; :disappointed:

anyway just add `joinToString(separator="")`