rfc:pipe-operator
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rfc:pipe-operator [2016/04/30 18:50] – Add ocramius' PSR7 example pollita | rfc:pipe-operator [2017/09/06 03:33] – Definition fixes and examples haskellcamargo | ||
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====== PHP RFC: Pipe Operator ====== | ====== PHP RFC: Pipe Operator ====== | ||
- | * Version: 0.1 | + | * Version: 0.3 |
* Date: 2016-04-29 | * Date: 2016-04-29 | ||
- | * Author: Sara Golemon < | + | * Author: Sara Golemon < |
* Status: Under Discussion | * Status: Under Discussion | ||
* First Published at: http:// | * First Published at: http:// | ||
Line 8: | Line 8: | ||
===== Introduction ===== | ===== Introduction ===== | ||
- | Complex nested expressions can become progressively difficult to read the deeper they go with function returns leading | + | A common PHP OOP pattern is the use of method chaining, or what is also known as " |
- | ===== Proposal ===== | + | For example, the following shows a SQL query expression built out of component pieces, then executed: |
- | Introduce the "Pipe Operator" | + | <code php> |
+ | $rs = $db | ||
+ | -> | ||
+ | -> | ||
+ | -> | ||
+ | -> | ||
+ | -> | ||
+ | </ | ||
- | This feature is being culled from HackLang 3.13 and the manual page for it may be referenced | + | This works well enough |
- | ==== PSR7 Example ==== | + | While decomposing these expressions to make use of multiple variables is an option, this can lead to reduced readability, |
- | Here's the pseudo-code for a typical | + | <code php> |
+ | $config = loadConfig(); | ||
+ | $dic = buildDic($config); | ||
+ | $app = getApp($dic); | ||
+ | $router = getRouter($app); | ||
+ | $dispatcher = getDispatcher($router, | ||
+ | $logic = dispatchBusinessLogic($dispatcher, | ||
+ | $render = renderResponse($logic); | ||
+ | $psr7 = buildPsr7Response($render); | ||
+ | $response | ||
+ | </ | ||
- | $request = getGlobals() | + | Or: |
- | |> parseRequest($$) | + | |
- | |> buildPsr7Request($$); | + | |
- | | + | <code php> |
- | |> buildDic($$) | + | $x = loadConfig(); |
- | |> getApp($$) | + | $x = buildDic($x); |
- | |> getRouter($app) | + | $x = getApp($x); |
- | |> getDispatcher($$, $request) | + | $x = getRouter($x); |
- | |> dispatchBusinessLogic($$, $request, new Response()) | + | $x = getDispatcher($x, $request); |
- | |> renderResponse($$) | + | $x = dispatchBusinessLogic($x, $request, new Response()); |
- | |> buildPsr7Response($$) | + | $x = renderResponse($x); |
- | |> emit($$); | + | $x = buildPsr7Response($x); |
+ | $response = emit($x); | ||
+ | </ | ||
- | Here's what it would look like with a separate approach (more business-oriented): | + | This may lead to error prone code, enforcing reassigment or pollution of the scope for readability. These sorts of chains could also, conceivably, |
- | buildRequest() // (basically the first part of the previous example here) | + | <code php> |
- | |> validate($$) | + | $dispatcher = getDispatcher(getRouter(getApp(buildDic(loadConfig()))), $request); |
- | |> convertToCommand($$) | + | $response = emit(buildPsr7Response(renderResponse(dispatchBusinessLogic($dispatcher, |
- | |> execute($$) | + | </ |
- | |> convertToViewModel($$) | + | |
- | |> render($$) | + | |
- | |> convertToHttpResponse($$) | + | |
- | | + | |
- | ==== File collection Example ==== | + | This RFC aims to improve code readability by bringing fluent expressions to functional and OOP libraries not originally designed for the task. Several languages already provide support for the pipe operator or, at least, for definining it. Some of the languages that offer support are Elixir, F#, LiveScript and HackLang. |
- | As an example, consider the following real block of code I wrote while creating a test importer (to migrate HHVM format tests into PHPT format): | + | ===== Proposal ===== |
+ | |||
+ | Introduce the "Pipe Operator" | ||
+ | |||
+ | This feature has already been implemented in HackLang, and the manual page for it may be referenced at: https:// | ||
+ | |||
+ | ==== PSR7 Example ==== | ||
+ | |||
+ | Here's the equivalent chain of function calls as demonstrated in the intro section above: | ||
+ | |||
+ | <code php> | ||
+ | $response = loadConfig() | ||
+ | |> buildDic($$) | ||
+ | |> getApp($$) | ||
+ | |> getRouter($$) | ||
+ | |> getDispatcher($$, | ||
+ | |> dispatchBusinessLogic($$, | ||
+ | |> renderResponse($$) | ||
+ | |> buildPsr7Response($$) | ||
+ | |> emit($$); | ||
+ | </ | ||
+ | |||
+ | ==== File Collection Example ==== | ||
+ | |||
+ | As an example, consider the following real block of code I wrote while creating a test importer (to migrate HHVM format tests into PHPT format). Please try not to get hung up into whether or not it's " | ||
- | | + | <code php> |
- | array_merge( | + | $ret = |
- | $ret, | + | array_merge( |
- | getFileArg( | + | $ret, |
- | array_map( | + | getFileArg( |
- | function ($x) use ($arg) { return $arg . '/' | + | array_map( |
- | array_filter( | + | function ($x) use ($arg) { return $arg . '/' |
- | scandir($arg), | + | array_filter( |
- | function ($x) { return $x !== ' | + | scandir($arg), |
- | ) | + | function ($x) { return $x !== ' |
) | ) | ||
) | ) | ||
- | ); | + | |
+ | | ||
+ | </ | ||
This block of code is readable, but one must carefully examine the nesting to determine what the initial input it, and what order it traverses the steps involved. | This block of code is readable, but one must carefully examine the nesting to determine what the initial input it, and what order it traverses the steps involved. | ||
- | With this proposal, the above could be rewritten as: | + | With this proposal, the above could be easily |
- | | + | <code php> |
- | |> array_filter($$, | + | $ret = scandir($arg) |
- | |> array_map(function ($x) use ($arg) { return $arg . '/' | + | |> array_filter($$, |
- | |> getFileArg($$) | + | |> array_map(function ($x) use ($arg) { return $arg . '/' |
- | |> array_merge($ret, | + | |> getFileArg($$) |
+ | |> array_merge($ret, | ||
+ | </ | ||
- | This clearly, and unambiguously shows `scandir()` as the initial source of data, that it goes through an `array_filter` to avoid recursion, an `array_map` to requalify the paths, some local function, and finally a merge to combine the result with a collector variable. | + | This, cleary |
+ | |||
+ | ==== FBShipIt Example ==== | ||
+ | |||
+ | Also consider [[https:// | ||
+ | |||
+ | <code php> | ||
+ | return $changeset | ||
+ | |> self:: | ||
+ | |> self:: | ||
+ | $$, | ||
+ | $config[' | ||
+ | ) | ||
+ | |> self:: | ||
+ | |> self:: | ||
+ | |> self:: | ||
+ | |> self:: | ||
+ | |> ShipItUserFilters:: | ||
+ | $$, | ||
+ | FBToGitHubUserInfo:: | ||
+ | ) | ||
+ | |> self:: | ||
+ | $$, | ||
+ | $config[' | ||
+ | ?? self:: | ||
+ | ) | ||
+ | |> self:: | ||
+ | |> self:: | ||
+ | |> self:: | ||
+ | </ | ||
+ | |||
+ | This presents every step taken by the common filter chain in an easy to follow list of actions. | ||
===== Backward Incompatible Changes ===== | ===== Backward Incompatible Changes ===== | ||
Line 80: | Line 151: | ||
While most ambiguities of `$$` between pipe replacement variable and variable variables are covered in the lexer rule, the following case is not accounted for: | While most ambiguities of `$$` between pipe replacement variable and variable variables are covered in the lexer rule, the following case is not accounted for: | ||
- | | + | <code php> |
- | $b = ' | + | $a = 1; |
- | var_dump($$ /* comment */ {' | + | $b = ' |
- | // Expected: int(1) | + | var_dump($$ /* comment */ {' |
- | // Actual: Use of $$ outside of a pipe expression | + | // Expected: int(1) |
+ | // Actual: Use of $$ outside of a pipe expression | ||
+ | </ | ||
- | This particular quirk of the parser (allowing comments in the middle of a variable-variable-brace-expression) is doubtlessly a rare occurance | + | This particular quirk of the parser (allowing comments in the middle of a variable-variable-brace-expression) is doubtlessly a rare occurrence |
Potential resolutions: | Potential resolutions: | ||
- | * Use a less-ambiguous token. | + | * Use a less-ambiguous token. `$>`, which mirrors `|>`, is my personal favorite. Downshot: doesn' |
- | * Get very creative in the parser. | + | * Get very creative in the parser. Since ' |
- | Note that HHVM does not handle this case either. | + | Note that HHVM does not handle this case either. Nor, in fact, does it handle mere whitespace between `$$` and `{expr}`, which the attached PHP implementation does. |
- | **Update:** HackLang is normally supposed to disallow variable-variables, | + | **Update:** HackLang is normally supposed to disallow variable-variables, |
===== Proposed PHP Version(s) ===== | ===== Proposed PHP Version(s) ===== | ||
- | 7.Next | + | 7.2 |
===== Open Issues ===== | ===== Open Issues ===== | ||
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===== Future Scope ===== | ===== Future Scope ===== | ||
- | The current proposal limits use of the `$$` to a single replacement per expression. | + | The current proposal limits use of the `$$` to a single replacement per expression. This feature could potentially be expanded to allow multiple uses of `$$` within a single RHS expression. |
+ | |||
+ | ===== Third-party Arguments ===== | ||
+ | |||
+ | Informal Twitter poll (821 respondents) results: https:// | ||
+ | |||
+ | * 62% "Love It" | ||
+ | * 24% " | ||
+ | * 14% "Hate It" | ||
+ | |||
+ | ==== In favor ==== | ||
+ | |||
+ | * Produces cleaner, more readable code, in order the things are executed | ||
+ | * Doesn' | ||
+ | * Enforces immutability and data transformation, | ||
+ | |||
+ | ==== Against ==== | ||
+ | |||
+ | * The new tokens are inobvious and difficult to google for | ||
+ | * Pipe chaining in other languages follows different rules \\ (e.g. implicit first arg, rather than explicit placeholder) | ||
+ | * Potentially confusing with variable-variables | ||
+ | * No opportunity for error catching/ | ||
+ | * Can be implemented using intermediate variables | ||
===== Proposed Voting Choices ===== | ===== Proposed Voting Choices ===== | ||
- | Adopt the PIpe Operator yes/ | + | Adopt the Pipe Operator yes/ |
===== Patches and Tests ===== | ===== Patches and Tests ===== |
rfc/pipe-operator.txt · Last modified: 2017/09/22 13:28 by 127.0.0.1