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[CLJ-1449] Add clojure.string functions for portability to ClojureScript Created: 19/Jun/14  Updated: 31/Jul/15

Status: Open
Project: Clojure
Component/s: None
Affects Version/s: Release 1.6
Fix Version/s: Release 1.8

Type: Enhancement Priority: Major
Reporter: Bozhidar Batsov Assignee: Nola Stowe
Resolution: Unresolved Votes: 29
Labels: ft, string

Attachments: Text File add_functions_to_strings-2.patch     Text File add_functions_to_strings-3.patch     Text File add_functions_to_strings-4.patch     Text File add_functions_to_strings-5.patch     Text File add_functions_to_strings-6.patch     Text File add_functions_to_strings.patch     Text File clj-1449-more-v1.patch    
Patch: Code
Approval: Vetted

 Description   

It would be useful if a few common functions from Java's String were available as Clojure functions for the purposes of increasing portability to other Clojure platforms like ClojureScript.

The functions below also cover the vast majority of cases where Clojure users currently drop into Java interop for String calls - this tends to be an issue for discoverability and learning. While the goal of this ticket is increased portability, improving that is a nice secondary benefit.

Proposed clojure.string fn java.lang.String method
index-of indexOf
last-index-of lastIndexOf
starts-with? startsWith
ends-with? endsWith
includes? contains

Patch:

  • add_functions_to_strings-4.patch - uses -1 to indicate not-found in index-of
  • add_functions_to_strings-6.patch - uses nil to indicate not-found in index-of

Performance: Tested the following with criterium for execution mean time (all times in ns).

Java Clojure Java Clojure (-4 patch) Clojure (-6 patch)
(.indexOf "banana" "n") (clojure.string/index-of "banana" "n") 8.70 9.03 9.27
(.indexOf "banana" "n" 1) (clojure.string/index-of "banana" "n" 1) 7.29 7.61 7.66
(.indexOf "banana" (int \n)) (clojure.string/index-of "banana" \n) 5.34 6.20 6.20
(.indexOf "banana" (int \n) 1) (clojure.string/index-of "banana" \n 1) 5.38 6.19 6.24
(.startsWith "apple" "a") (clojure.string/starts-with? "apple" "a") 4.84 5.71 5.65
(.endsWith "apple" "e") (clojure.string/ends-with? "apple" "e") 4.82 5.68 5.70
(.contains "baked apple pie" "apple") (clojure.string/includes? "baked apple pie" "apple") 10.78 11.99 12.17

Screened by:

Note: In both Java and JavaScript, indexOf will return -1 to indicate not-found, so this is (at least in these two cases) the status quo. The benefit of nil return in Clojure is that it can be used as a found/not-found condition. The benefit of a -1 return is that it matches Java/JavaScript and that the return type can be hinted as a primitive long, allowing you to feed it into some other arithmetic or string operation without boxing.



 Comments   
Comment by Alex Miller [ 19/Jun/14 12:53 PM ]

Re substring, there is a clojure.core/subs for this (predates the string ns I believe).

clojure.core/subs
([s start] [s start end])
Returns the substring of s beginning at start inclusive, and ending
at end (defaults to length of string), exclusive.

Comment by Jozef Wagner [ 20/Jun/14 3:21 AM ]

As strings are collection of characters, you can use Clojure's sequence facilities to achieve such functionality:

user=> (= (first "asdf") \a)
true
user=> (= (last "asdf") \a)
false
Comment by Alex Miller [ 20/Jun/14 8:33 AM ]

Jozef, String.startsWith() checks for a prefix string, not just a prefix char.

Comment by Bozhidar Batsov [ 20/Jun/14 9:42 AM ]

Re substring, I know about subs, but it seems very odd that it's not in the string ns. After all most people will likely look for string-related functionality in clojure.string. I think it'd be best if `subs` was added to clojure.string and clojure.core/subs was deprecated.

Comment by Pierre Masci [ 01/Aug/14 5:27 AM ]

Hi, I was thinking the same about starts-with and .ends-with, as well as (.indexOf s "c") and (.lastIndexOf "c").

I read the whole Java String API recently, and these 4 functions seem to be the only ones that don't have an equivalent in Clojure.
It would be nice to have them.

Andy Fingerhut who maintains the Clojure Cheatsheet told me: "I maintain the cheatsheet, and I put .indexOf and .lastIndexOf on there since they are probably the most common thing I saw asked about that is in the Java API but not the Clojure API, for strings."
Which shows that there is a demand.

Because Clojure is being hosted on several platforms, and might be hosted on more in the future, I think these functions should be part of the de-facto ecosystem.

Comment by Andy Fingerhut [ 30/Aug/14 3:39 PM ]

Updating summary line and description to add contains? as well. I can back this off if it changes your mind about triaging it, Alex.

Comment by Andy Fingerhut [ 30/Aug/14 3:40 PM ]

Patch clj-1449-basic-v1.patch dated Aug 30 2014 adds starts-with? ends-with? contains? functions to clojure.string.

Patch clj-1449-more-v1.patch is the same, except it also replaces several Java method calls with calls to these Clojure functions.

Comment by Andy Fingerhut [ 05/Sep/14 1:02 PM ]

Patch clj-1449-basic-v1.patch dated Sep 5 2014 is identical to the patch I added recently called clj-1149-basic-v1.patch. It is simply renamed without the typo'd ticket number in the file name.

Comment by Yehonathan Sharvit [ 02/Dec/14 3:09 PM ]

What about an implementation that works also in cljs?

Comment by Bozhidar Batsov [ 02/Dec/14 3:11 PM ]

Once this is added to Clojure it will be implemented in ClojureScript as well.

Comment by Yehonathan Sharvit [ 02/Dec/14 3:22 PM ]

Great! Any idea when it will be added to Clojure?
Also, will it be automatically added to Clojurescript or someone will have to write a particular code for it.
The suggested patch relies on Java so I am curious to understand who is going to port the patch to cljs.

Comment by Bozhidar Batsov [ 02/Dec/14 3:27 PM ]

No idea when/if this will get merged. Upvote the ticket to improve the odds of this happening sooner.
Someone on the ClojureScript team will have to implement this in terms of JavaScript.

Comment by Alex Miller [ 02/Dec/14 4:01 PM ]

Some things that would be helpful:

1) It would be better to combine the two patches into a single patch - I think changing current uses into new users is a good thing to include. Also, please keep track of the "current" patch in the description.
2) Patch needs tests.
3) Per the instructions at the top of the clojure.string ns (and the rest of the functions), the majority of these functions are implemented to take the broader CharSequence interface. Similar to those implementations, you will need to provide a CharSequence implementation while also calling into the String functions when you actually have a String.
4) Consider return type hints - I'm not sure they're necessary here, but I would examine bytecode for typical calling situations to see if it would be helpful.
5) Check performance implications of the new versions vs the old with a good tool (like criterium). You've put an additional var invocation and (soon) type check in the calling path for these functions. I think providing a portable target is worth a small cost, but it would be good to know what the cost actually is.

I don't expect we will look at this until after 1.7 is released.

Comment by Andy Fingerhut [ 02/Dec/14 8:05 PM ]

Alex, all your comments make sense.

If you think a ready-and-waiting patch that does those things would improve the odds of the ticket being vetted by Rich, please let us know.

My guess is that his decision will be based upon the description, not any proposed patches. If that is your belief also, I'll wait until he makes that decision before working on a patch. Of course, any other contributor is welcome to work on one if they like.

Comment by Alex Miller [ 02/Dec/14 8:40 PM ]

Well nothing is certain of course, but I keep a special report of things I've "screened" prior to vetting that makes possible moving something straight from Triaged all the way through into Screened/Ok when Rich is able to look at them. This is a good candidate if things were in pristine condition.

That said, I don't know whether Rich will approve it or not, so it's up to you. I think the argument for portability is a strong one and complements the feature expression.

Comment by Alex Miller [ 14/May/15 8:55 AM ]

I'd love to have a really high-quality patch on this ticket to consider for 1.8 that took into account my comments above.

Also, it occurred to me that I don't think this should be called "contains?", overlapping the core function with a different meaning (contains value vs contains key). Maybe "includes?"?

Comment by Andy Fingerhut [ 14/May/15 9:14 AM ]

clojure.string already has 2 name conflicts with clojure.core, for which most people probably do something like (require '[clojure.string :as str]) to avoid that:

user=> (use 'clojure.string)
WARNING: reverse already refers to: #'clojure.core/reverse in namespace: user, being replaced by: #'clojure.string/reverse
WARNING: replace already refers to: #'clojure.core/replace in namespace: user, being replaced by: #'clojure.string/replace
nil
Comment by Alex Miller [ 14/May/15 10:05 AM ]

I'm not concerned about overlapping the name. I'm concerned about overlapping it and meaning something different, particularly vs one of the most confusing functions in core already. clojure.core/contains? is better than linear time key search. clojure.string/whatever will be a linear time subsequence match.

Comment by Alex Miller [ 14/May/15 10:18 AM ]

Ruby uses "include?" for this.

Comment by Devin Walters [ 19/May/15 4:56 PM ]

I agree with Alex's comment about the overlap. Personally, I prefer the way "includes?" reads over "include?", but IMO either one is better than adding to the "contains?" confusion.

Comment by Bozhidar Batsov [ 20/May/15 12:10 AM ]

I'm fine with `includes?`. Ruby is famous for the bad English used in its core library.

Comment by Andrew Rosa [ 17/Jun/15 12:29 PM ]

Andy Fingerhut, since you are the author of the original patch do you desire to continue the work on it? If you prefer (or even need) to focus on different stuff, I would like to tackle this issue.

Comment by Andy Fingerhut [ 17/Jun/15 1:08 PM ]

Andrew Rosa, I am perfectly happy if someone else wants to work on a revised patch for this. If you are interested, go for it! And from Alex's comments, I believe my initial patch covers such a small fraction of what he wants, do not worry about keeping my name associated with any patch you submit – if yours is accepted, my patch will not have helped you in getting there.

Comment by Nola Stowe [ 03/Jul/15 9:01 AM ]

Andrew Rosa, I am interested on working on this. Are you currently working it?

Comment by Andrew Rosa [ 03/Jul/15 12:08 PM ]

Thanks Andy Fingerhut, didn't saw the answer here. I'm happy that Nola Stowe could take this one.

Comment by Nola Stowe [ 08/Jul/15 12:46 PM ]

Updated patch to rename methods as specified and add tests.

Comment by Bozhidar Batsov [ 08/Jul/15 3:26 PM ]

A few remarks:

1. added should say 1.8, not 1.9.
2. The docstrings could be improved a bit - normally they should end with a . and refer to all the params of the function in question.

Comment by Nola Stowe [ 08/Jul/15 3:29 PM ]

Thanks Bozhidar Batsov .. I will, and I also got feedback from the slack clojure-dev group (Alex, Ghadi, AndrewHr) so I will be submitting an improved patch soon

Comment by Andy Fingerhut [ 09/Jul/15 11:57 AM ]

Also, I am not sure, but Alex Miller made this comment earlier: "Per the instructions at the top of the clojure.string ns, functions should take the broader CharSequence interface instead of String. Similar to existing clojure.string functions, you will need to provide a CharSequence implementation while also calling into the String functions when you actually have a String."

Looking at the Java classes and interfaces, one of the classes that implements CharSequence is CharBuffer, and it has no indexOf or lastIndexOf methods. If one were to call the proposed index-of or last-index-of with a CharBuffer, I believe you would get an exception for an unknown method.

I don't know if Alex's sentence is essential to any patch to be considered, but wanted to point out that it seems like it effectively means writing your own implementation of each of these methods for some of the classes implementing the CharSequence interface.

Comment by Nola Stowe [ 09/Jul/15 4:15 PM ]

Andy, yes you are right. Alex helped me with my current changes (not posted yet) and where needed I cast the value to a string so that it would have the indexOf methods.

Comment by Nola Stowe [ 10/Jul/15 7:43 AM ]

Added type hints, using StringBuffer instead of string in tests.

Comment by Nola Stowe [ 10/Jul/15 11:53 PM ]

Use critium and did some bench marking, I am not familiar enough to say "hey its good or no, too slow". I tried an optimization but it didn't make much difference.

notes here:

https://www.evernote.com/l/ABLYZbDr8ElIs6fkODAd3poBfIm_Bfr5kLo

Appreciate any feedback

Comment by Alex Miller [ 13/Jul/15 10:37 AM ]

Nola, some comments:

1) In index-of and last-index-of, I think we should use (instance? Character value) instead of char? - this will avoid a function invocation.

2) In index-of and last-index-of, in the branches where you know you have a Character, we should just invoke the proper function on the character instance directly rather than calling int. In this case that is (.charValue ^Character value). However, this function returns char so you still want the ^int hint.

3) In index-of and last-index-of, we should do a couple of things to maximally utilize primitive support for from-index. We should type-hint the incoming value as a ^long (only long and double are specialized cases in Clojure, not int). We should then use the function unchecked-int to optimally convert the long primitive to an int primitive.

4) We should type-hint the return value to a primitive long to avoid boxing the return.

Putting 1+2+3+4 together:

(defn index-of
  "Return index of value (string or char) in s, optionally searching forward from from-index."
  {:added "1.8"}
  (^long [^CharSequence s value]
   (if (instance? Character value)
     (.indexOf (.toString s) ^int (.charValue ^Character value))
     (.indexOf (.toString s) ^String value)))
  (^long [^CharSequence s value ^long from-index]
  (if (instance? Character value)
    (.indexOf (.toString s) ^int (.charValue ^Character value) (unchecked-int from-index))
    (.indexOf (.toString s) ^String value (unchecked-int from-index)))))

Similar changes in last-index-of.

5) In starts-with? and ends-with?, I would move the type hint for substr to the parameter declaration. This is more of a style preference on my part, no functional difference I believe.

6) On includes? I would do the same as #5, except .contains actually takes a CharSequence for the substr, so I would change the type hint from ^String to the broader ^CharSequence.

7) Can you edit the description and add a table with the "execution time mean" number for direct Java vs new Clojure fn for the patch after these changes? Please add tests for the from-index variants of index-of and last-index-of as well.

Comment by Nola Stowe [ 14/Jul/15 5:46 PM ]

optimizations as suggested by Alex Miller

Comment by Andy Fingerhut [ 14/Jul/15 5:50 PM ]

Nola, not a big deal, but Rich has requested that patch file names end with ".patch" or ".diff", I think because whatever he uses to view them recognizes that suffix and puts it in a different viewing/editing mode.

Comment by Nola Stowe [ 14/Jul/15 6:03 PM ]

Andy, so no need to keep around patches when used in comparisons?

Comment by Andy Fingerhut [ 14/Jul/15 8:31 PM ]

It is ok to have multiple versions of patches attached, but names like add_functions_to_strings-2.patch etc. would be preferred over names like add_functions_to_strings.patch-2, so the suffix is ".patch".

Comment by Nola Stowe [ 14/Jul/15 8:55 PM ]

original patch submitted by Nola

Comment by Nola Stowe [ 14/Jul/15 8:56 PM ]

Optimizations suggested by Alex

Comment by Alex Miller [ 14/Jul/15 9:44 PM ]

Nola, I re-did the timings on my machine - these were done with Java 1.8 and no Leiningen involved.

Comment by Alex Miller [ 14/Jul/15 9:57 PM ]

-4 patch is identical to -3 but removes one errant ^long type hint

Otherwise, looks good to me!

Comment by Alex Miller [ 17/Jul/15 10:24 PM ]

Rich, since you didn't put any comments on here, I'm not sure if there's anything else you wanted, so marking screened.

Comment by Stuart Halloway [ 19/Jul/15 7:36 AM ]

I dislike the approach here for several reasons:

  • floats Java-isms (-1 for missing instead of nil?) up into the Clojure API
  • makes narrow string fns out of things that could/should be seq fns

Stepping back, this is all library work. Why should it be in core? If this started in a contrib, it could evolve much more freely.

Comment by Alex Miller [ 19/Jul/15 8:49 AM ]

re Java-isms: totally fair comment worth changing

re narrow string fns: if these were seq fns, they would presumably take seqables of chars and return seqables of chars. When I have strings, I want to work with strings (as with clojure.string/join and clojure.string/reverse vs their seq equivalents).

re library: these particular functions are the most commonly used string functions where current users drop to Java interop. Note that all 5 of these functions have over time been added to the cheatsheet (http://clojure.org/cheatsheet) because they are commonly used. I believe there is significant value in including them in core and standardizing their name and behavior across to CLJS.

Comment by Bozhidar Batsov [ 19/Jul/15 10:29 AM ]

I'm obviously biased, but I totally agree with everything Alex said. Having one core string library and a separate contrib string library is just impractical. With clojure.string already part of the language it's much more sensible to extend it where/when needed instead of encouraging the proliferation of tons of alternative libraries (there are already a couple of those out there, mostly because essential functions are missing). Initial designs are rarely perfect, there's nothing wrong in revisiting and improving them.

I believe this is one of the top voted tickets, which clearly indicates that the Clojure community is quite supportive of this additions.

Comment by Michael Blume [ 19/Jul/15 12:26 PM ]

None of these functions return Strings so they could very easily be seq functions which use the String methods as a fast path when called with Strings, the trouble is then they wouldn't necessarily belong in clojure.string.

Comment by Bozhidar Batsov [ 19/Jul/15 1:49 PM ]

Such an argument can be made for existing functions like clojure.core/subs and clojure.string/reverse - we could have just went with generic functions that operate on seqs and converted the results to strings, but we didn't. It might be just me, but I'm really thinking this is being overanalysed. Sometimes it's really preferable to deal with some things as strings (not to mention more efficient).

Comment by Rich Hickey [ 20/Jul/15 9:39 AM ]

I completely agree with Alex and Bozhidar re: strings vs seqs. Other langs that have only lists and use them for strings are really bad at strings. So - string-specific fns are ok. What about the Java-isms?

Comment by Bozhidar Batsov [ 20/Jul/15 10:08 AM ]

We should address them for sure. Let's wait for a couple of days for Nola to update the patch. If she's too busy I'll do the update myself.

Comment by Nola Stowe [ 20/Jul/15 10:50 AM ]

I will be happy to work on it Saturday. Is nil an acceptable response when index-of "apple" "p" is not found? The other functions return booleans and I think those are ok.

Comment by Bozhidar Batsov [ 20/Jul/15 10:55 AM ]

Yep, we should go with nil.

Comment by Nola Stowe [ 25/Jul/15 4:33 PM ]

Changed index-of and last-index-of to return nil instead of -1 (java-ism), thus had to remove the type hint for the return value.

Seems to have slowed down the function compared to having the function return -1. My benchmarks: https://www.evernote.com/l/ABL2wead73BJZYAkpH5yxsfX9JM8cpUiNhw

Comment by Nola Stowe [ 25/Jul/15 9:05 PM ]

Updated patch to include return value in doc string for index-of last-index-of, otherwise same as last update.

Comment by Alex Miller [ 26/Jul/15 8:40 AM ]

Removing the hint causes the return type to be Object, which forces boxing in the "found" cases.

Comment by Nola Stowe [ 26/Jul/15 8:56 AM ]

Is it worth it to remove the java-ism of returning -1 when not found? Personally, I don't really like a function returning one of two things... found index or nil ... I prefer it being an int at all times.

Comment by Alex Miller [ 26/Jul/15 9:00 AM ]

There is one whitespace issue in the -5 patch:

[~/code/clojure (master)]$ git apply ~/Downloads/add_functions_to_strings-5.patch
/Users/alex/Downloads/add_functions_to_strings-5.patch:34: trailing whitespace.
  (let [result
warning: 1 line adds whitespace errors.

I updated the timings in the description to include both -4 and -5 - the boxing there does have a significant impact.

Comment by Nola Stowe [ 26/Jul/15 9:28 AM ]

Fixed whitespace issue.

Comment by Alex Miller [ 26/Jul/15 9:32 AM ]

Added -6 patch and timings that address most of the performance impact.

Comment by Stuart Halloway [ 27/Jul/15 9:35 AM ]

Alex: Note that all of these functions return numbers and booleans, not strings nor seqs of anything. This is partially why they were left out of the original string implementation.

It isn't clear to me why index-of should be purely a string fn, I regularly need index-of with other things, and both my book and JoC use index-of as an example of a nice-to-have.

Comment by Nicola Mometto [ 27/Jul/15 9:44 AM ]

Stuart, I don't think the fact that those functions don't return string is really relevant, the important fact is that they operate on strings (just like c.set/superset? or subset? don't return sets) and are frequently used on them.

Comment by Bozhidar Batsov [ 27/Jul/15 9:51 AM ]

I'm with Nicola on this one - we have to be practical. There's a reason why this is the top-voted JIRA ticket - Clojure programmers want those functions. That's says plenty.

Anyways, having a generic `index-of` is definitely not a bad idea.

Comment by Stuart Halloway [ 31/Jul/15 11:27 AM ]

How does this compare to making them all seq fns and adding them to clojure.core?

Comment by Andy Fingerhut [ 31/Jul/15 11:39 AM ]

Given Rich's comment earlier "I completely agree with Alex and Bozhidar re: strings vs seqs. Other langs that have only lists and use them for strings are really bad at strings. So - string-specific fns are ok.", do we need to write a separate patch that makes these all into seq fns and do performance comparisons between those vs. the string-specific ones?

Comment by Stuart Halloway [ 31/Jul/15 1:26 PM ]

Andy,

Definitely not! I want to have a design conversation.

We have protocols, and could use them to provide core fns that are specialized to strings, so it isn't clear to me why we would have to be really bad at it.

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