chore: use $ReadOnlyArray when input array is not modified (fixes #84)

[gajus]

No description provided.

[gajus]

As far as I can tell, these are the only safe changes.

I have left output type as Array as that would be a breaking change/ outside of scope.

I have left comments as Array since $ReadOnlyArray is a sub-type of Array.

cc @wincent

[gajus]

The build process is failing because of:

/home/travis/build/facebook/dataloader/src/index.js
   13:1   error  Line 13 exceeds the maximum line length of 80  max-len
   13:33  error  '$ReadOnlyArray' is not defined                no-undef
   13:63  error  '$ReadOnlyArray' is not defined                no-undef
  133:18  error  '$ReadOnlyArray' is not defined                no-undef
  309:26  error  '$ReadOnlyArray' is not defined                no-undef

Have you considered using https://github.com/gajus/eslint-plugin-flowtype?

I have added $ReadOnlyArray to globals as an interim fix.

[coveralls]

Coverage remained the same at 100.0% when pulling 8ce9138 on gajus:feat/use-readonlyarray into 75a0dfb on facebook:master.

[wincent]

Thanks @gajus. Will merge with a couple of tweaks applied on top.

[gajus]

Regarding feee2aa, that was an ESLint error, not Flow.

[gajus]

No idea how this got into the PR. Sorry.

[wincent]

Regarding feee2aa, that was an ESLint error, not Flow.

Bah, should have waited for Travis...

[coveralls]

Coverage remained the same at 100.0% when pulling 8a8651a on gajus:feat/use-readonlyarray into 75a0dfb on facebook:master.

[gajus]

@wincent Can this be released please?

I am still getting dozens of:

Error: src/factories/createLoaders.js:267
267:     ReservationByReservationUidLoader: new DataLoader(getReservationByReservationUids),
                                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function. This type is incompatible with the expected param type of
 45:     batchLoadFn: BatchLoadFn<K, V>,
                      ^^^^^^^^^^^^^^^^^ function type. See: node_modules/dataloader/index.js.flow:45
  This parameter is incompatible:
    143:     return getByIdsLoader(connection, 'reservation', reservationUids, 'uid');
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type application of identifier `Promise`. Has some incompatible type argument with
     13: type BatchLoadFn<K, V> = (keys: Array<K>) => Promise<Array<V | Error>>;
                                                      ^^^^^^^^^^^^^^^^^^^^^^^^^ type application of identifier `Promise`. See: node_modules/dataloader/index.js.flow:13
      Type argument `R` is incompatible:
         42: ): Promise<$ReadOnlyArray<QueryResultRowType>> => {
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ read-only array type. This type is incompatible with. See: src/utilities/getByIdsLoader.js:42
         13: type BatchLoadFn<K, V> = (keys: Array<K>) => Promise<Array<V | Error>>;
                                                                  ^^^^^^^^^^^^^^^^ array type. See: node_modules/dataloader/index.js.flow:13

It is really discouraging to contribute anything if it does not get released for months.

[gajus]

@leebyron Any comment here?