| | 1 | == Matching == |
| | 2 | Prefer named arguments:: |
| | 3 | When matching a uniontype, prefer using named arguments to only match what is used. A match using named arguments only needs to be changed if the matched fields change in a uniontype, while a match using positional arguments will always have to be changed if the uniontype changes. |
| | 4 | {{{#!mo |
| | 5 | // Prefer this. |
| | 6 | case DAE.ARRAY(ty = array_ty) |
| | 7 | |
| | 8 | // Not this. |
| | 9 | case DAE.ARRAY(array_ty, _, _) |
| | 10 | }}} |
| | 11 | One exception is when matching all fields in a uniontype, doing some changes to them, and then constructing a new instance of the same type. In that case the code will need to be updated if the uniontype changes anyway, so using positional arguments will give cleaner code. |
| | 12 | {{{#!mo |
| | 13 | case DAE.ARRAY(array_ty, is_scalar, expl) |
| | 14 | equation |
| | 15 | expl = listRest(expl); |
| | 16 | then |
| | 17 | DAE.ARRAY(array_ty, is_scalar, expl) |
| | 18 | }}} |
| | 19 | |
| | 20 | Use {{{else}}} for catch-all:: |
| | 21 | Prefer using {{{else}}} when writing a catch-all case: |
| | 22 | {{{#!mo |
| | 23 | outValue := match(inExp1, inExp2) |
| | 24 | local |
| | 25 | Integer i1, i2; |
| | 26 | |
| | 27 | case (DAE.ICONST(integer = i1), DAE.ICONST(integer = i2)) then i1 + i2; |
| | 28 | else 0; |
| | 29 | |
| | 30 | // Avoid this: |
| | 31 | case (_, _) then 0; |
| | 32 | // And this (using 'then' is legal, but unnecessary): |
| | 33 | else then 0; |
| | 34 | end match; |
| | 35 | }}} |
| | 36 | Use {{{as}}} only for partial matches:: |
| | 37 | {{{as}}} is usually not necessary when matching a whole input argument, such as this: |
| | 38 | {{{#!mo |
| | 39 | _ := match(inExp, inStr) |
| | 40 | local |
| | 41 | DAE.Exp exp; |
| | 42 | String str; |
| | 43 | |
| | 44 | case (exp as DAE.CALL(path = Absyn.IDENT("sum")), _) then ExpressionDump.printExpStr(exp); |
| | 45 | case (_, str as "someString") then str; |
| | 46 | end match; |
| | 47 | }}} |
| | 48 | Prefer using the input parameters directly instead: |
| | 49 | {{{#!mo |
| | 50 | _ := match(inExp, inStr) |
| | 51 | case (DAE.CALL(path = Absyn.IDENT("sum")), _) then ExpressionDump.printExpStr(inExp); |
| | 52 | case (_, "someString") then inStr; |
| | 53 | end match; |
| | 54 | }}} |
