Sdk: Add a Python-like slice operator for lists and strings

[justinfagnani]

String.substring() and List.getRange() are somewhat verbose, but very common operations. Python's slice operator provides an easy-to-read notation to replace these.

Examples of substring() and slice [:]

string.substring(a) -> string[a:]

string.substring(a, b) -> string[a:b]

string.substring(0, a) -> string[:a]

[dgrove]

_Removed Type-Defect label._
_Added Type-Enhancement, Area-Library, Triaged labels._

[DartBot]

_This comment was originally written by @jinmingjian_

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great. more my idea is to enhance the slicing operator to an general indexing technology for array like objects, like:

1: a:b = a:1:b = a,a+1,...,b
2: a:2:b = a, a+2,...b
3: a:-1:b = a, a-1,...b
4: [:,a:b] = [1,a:b],[2,a:b]...

[DartBot]

_This comment was originally written by [e-mail]_

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I would argue that it is not easier to read. substring says what it is doing in English, whereas string[3:2] is symbolism.

[DartBot]

_This comment was originally written by @jinmingjian_

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yes or no. Yes, because this is just a syntax magic. No, ":" for slicing is the tradition of numerical computing software[1]. My suggestion is more mathematical. That is, it does not pursue symbolism, it pursues intuition. The ":" is used for generating a vectorized index(i.e.,1D array). And,

1. the basic form is [start:step:end];
2. [start:end] is the simplified form of [start:1:end];
3. : is the simplified form of [head:tail];
4. generally, start<=end and step>0, but allow start>=end and step<0 makes reversed indexing easier.
5. get nothing if the index does not exist mathematically.

So,
[3:2] -> [3:1:2], 3 can not reach 2 by step 1 -> nothig. may want [3:-1:2]
[:a] -> not syntax right, may want [0:a]

[1] http://en.wikipedia.org/wiki/Array_slicing

[DartBot]

_This comment was originally written by @jinmingjian_

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numerical computing software -> numerical computing language, more exactly.

[DartBot]

_This comment was originally written by @seaneagan_

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I think this would require a user-definable operator:

List#getRange becomes:
List<T> operator :;

String#substring becomes:
String operator :;

And it would probably make sense to support slicing then as well, by replacing List#setRange with:

List<T> operator [:]= (List other, [int first, int last]);

List#removeRange also becomes unnecessary, instead of:

list.removeRange(0, 5);

just do:

list[:5] = [];
// or
list[:5] = null;

[floitschG]

Reassigning to language. This requires new syntax and is thus not a library bug.

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_Removed Area-Library label._
_Added Area-Language label._

[floitschG]

Issue #8977 has been merged into this issue.

[Zectbumo]

Please support negative indexes (relative from the end) as Python does.
At the very least make String.substring() accept negative indexes.

[gbracha]

_Set owner to @gbracha._
_Removed Priority-Medium label._
_Added Priority-Low, Accepted labels._

[deadsoul44]

It has been 8.5 years. substring method should accept negative values.

[Zectbumo]

Yeah, this is really weird since even Javascript String.prototype.slice() takes negative values.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/slice

[pauleohare]

Any news on this? Is it ever going to happen? Doesn't sound too difficult. Is it?