Add a function pipe operator

[DartBot]

This issue was originally filed by @chalin

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Both AngularDart and Polymer have special syntax in support of function pipes (for Filters and Transformers) through the pipe | (bar) operator. E.g.

    person.lastName | uppercase

It would seem a natural fit for Dart to have native support for such a pipe operator. A case for the addition of a pipe operator in Dart is given here: http://pchalin.blogspot.com/2014/02/case-for-pipe-operator-in-dart.html

As is mentioned in the blog entry, I believe that added support should be considered for function composition operators (forward and/or reverse) as well.

[DartBot]

This comment was originally written by @chalin

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It just occurred to me that Dart already supports operator definitions and that the bar (|) operator is among the supported operator symbols. I suppose then, that all we need is for the dart:core Function class to be enhanced with a bar operator definition.

[kevmoo]

Removed Type-Defect label.
Added Type-Enhancement, Area-Language, Triaged labels.

[DartBot]

This comment was originally written by @zoechi

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This is a nice idea but | is already in use for bitwise OR.

[DartBot]

This comment was originally written by @chalin

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Re #­1. On second thought, adding a bar operator to the Function class would not work since in an expression like x | F the receiver is x not F and hence bar would have to be declared for x. Thus to support this as a method, it would need to be added to Object, ... or given some special support by the compiler.

[DartBot]

This comment was originally written by @chalin

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Re #­3. There is no fixed prescriptive use of operators in Dart. I.e., Dart supports operator overloading see [1], Table 2.11. Operators that can be overridden. Notice that the bar operator is part of the list.

[1] https://www.dartlang.org/docs/dart-up-and-running/contents/ch02.html#classes-operators

[DartBot]

This comment was originally written by @vicb

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see https://code.google.com/p/dart/issues/detail?id=18485

[kevmoo]

Issue dart-lang/sdk#18485 has been merged into this issue.

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cc @gbracha.

[kevmoo]

Here's a vote for the F#-like "|>" syntax. We avoid overloading the behavior of bit-wise.

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Set owner to @gbracha.

[gbracha]

There are useful details in the duplicate issue dart-lang/sdk#18485. Something along these lines is definitely possible, but it will take time - not because it is hard, but because we now have a standards process.

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Added Accepted label.

[lrhn]

Issue dart-lang/sdk#18516 has been merged into this issue.

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cc @floitschG.

[DartBot]

This comment was originally written by @chalin

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Again, thanks for promoting function pipes Kevin. I agree that new syntax for piping makes more sense; I had originally proposed use of | because it matched what Angular and Polymer use.

but it will take time ... because we now have a standards process.

In that case, I would hope that the added support of function composition (mentioned at the end of the original entry for this issue) will be considered at the same time. Should I open a separate issue to track this?

[kevmoo]

RE #­11 from pchalin:

Please open a separate issue. We could offer method piping without providing a general model for method composition.

[DartBot]

This comment was originally written by @chalin

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Doen: https://code.google.com/p/dart/issues/detail?id=18522

[yjbanov]

Has anyone started or is anyone interested in starting a DEP for this?