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Fix #284: New Rule: Param Pattern Matching
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,21 @@ | ||
| # Param Pattern-Matching | ||
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| (since [3.0.0](https://github.com/inaka/elvis_core/releases/tag/3.0.0)) | ||
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| When capturing a parameter using pattern matching you can either put the parameter | ||
| name on the left (`Param = #{pattern := ToMatch}`) or right (`#{pattern := ToMatch} = Param`) side | ||
| of the pattern that you use in the function clause. | ||
| This rule will make sure you are consistent through your code and use always the same style. | ||
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| > Works on `.beam` file? Yes! | ||
| ## Options | ||
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| - `side :: left | right`. | ||
| - default: `left`. | ||
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| ## Example | ||
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| ```erlang | ||
| {elvis_style, param_pattern_matching, #{side => right}} | ||
| ``` |
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,24 @@ | ||
| -module(left_param_pattern_matching). | ||
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| -export([single/1, multiple/1, different_param/3, different_clause/1]). | ||
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| single(Simple = {left, side, assignment}) -> | ||
| fun(SimpleToo = {left, side, assignment}) -> Simple == SimpleToo end. | ||
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| multiple(Multiple = Assignments = {on, the, left, side}) -> | ||
| fun(MultipleToo = AssignmentsToo = {on, the, left, side}) -> | ||
| {Multiple, Assignments} == {MultipleToo, AssignmentsToo} | ||
| end. | ||
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| different_param(happens_on, TheSecond = #{param := of_the}, function) -> | ||
| fun(happens_on, TheSecondToo = #{param := of_the}, function) -> TheSecond == TheSecondToo | ||
| end. | ||
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| different_clause("it doesn't happen on the first clause") -> | ||
| not_here; | ||
| different_clause(But = "it does in the second one") -> | ||
| fun ("it doesn't happen on the first clause") -> | ||
| not_here; | ||
| (ButToo = "it does in the second one") -> | ||
| But == ButToo | ||
| end. |
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,19 @@ | ||
| -module(pass_param_pattern_matching_elvis_attr). | ||
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| -elvis([{elvis_style, param_pattern_matching, #{side => right}}]). | ||
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| -export([my_fun/1, my_fun/3]). | ||
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| my_fun(#{[variable, goes] := [on, the]} = Right) -> | ||
| fun (#{[variable, goes] := [on, the]} = RightToo) -> | ||
| Right == RightToo; | ||
| ({can, be, Left} = {_If, _It, "is not a single variable"}) -> | ||
| Left | ||
| end; | ||
| my_fun({can, be, Left} = {_If, _It, "is not a single variable"}) -> | ||
| Left. | ||
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| my_fun(works, {as, well, on} = TheOther, parameters) -> | ||
| fun(works, {as, well, on} = TheOtherToo, parameters) -> | ||
| TheOther == TheOtherToo | ||
| end. |
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,41 @@ | ||
| -module(right_param_pattern_matching). | ||
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| -export([single/1, multiple/1, different_param/3, different_clause/1]). | ||
| -export([regular_matching_works_fine/0]). | ||
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| single({right, side, assignment} = Simple) -> | ||
| fun({right, side, assignment} = SimpleToo) -> Simple == SimpleToo end. | ||
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| %% This is not a match. According to Erlang precedence rules, the following code is actually | ||
| %% equivalent to: {on, the, right, side} = (Multiple = Assignments). | ||
| %% It's a tuple against a match, not a tuple against a variable against another variable | ||
| %% That's why no warnings are emitted for this line even if side is 'left'. | ||
| multiple({on, the, right, side} = Multiple = Assignments) -> | ||
| fun({on, the, right, side} = MultipleToo = AssignmentsToo) -> | ||
| {Multiple, Assignments} == {MultipleToo, AssignmentsToo} | ||
| end. | ||
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| different_param(happens_on, #{the_second := param_of} = The, function) -> | ||
| fun(happens_on, #{the_second := param_of} = TheToo, function) -> The == TheToo | ||
| end. | ||
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| different_clause("it doesn't happen on the first clause") -> | ||
| not_here; | ||
| different_clause("it does in the second one" = AsYoda) -> | ||
| fun ("it doesn't happen on the first clause") -> | ||
| not_here; | ||
| ("it does in the second one" = AsYodaToo) -> | ||
| AsYoda == AsYodaToo | ||
| end. | ||
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| regular_matching_works_fine() -> | ||
| This = works:fine(), | ||
| case This of | ||
| This = #{is := also} -> | ||
| valid; | ||
| _ -> | ||
| fun() -> | ||
| Like = This, | ||
| valid:as_well(Like) | ||
| end | ||
| end. |
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