> Furthermore, this probably comes up most commonly with dictionaries, since
> they're a sequence of tuples. The element tuple for dictionaries has element
> labels (key: Key, value: Value), so instead of writing `{ tuple in let (key,
> value) = tuple; f(key, value) }`, you could use the implicit argument and
> write `{ f($0.key, $0.value) }`.
>
> -Joe
I've migrated a project from Swift 3 to Swift 4 (relevant commit:
https://github.com/groue/GRDB.swift/commit/4f26cbcacf7b783c9c503f2909f2eb03ef7930fe)
Joe is right, dictionaries, as handy as they are, are particularly affected.
But $0 is hardly a panacea.
What I regret the most with the change is the lost ability to give *relevant
names* to tuple elements (and sometimes with the forced introduction of a phony
variable that has no relevant name (like "pair").
Here are below four examples of regressions introduced by SE-0110:
Example 1
- return columns.index { (column, _) in column.lowercased() ==
lowercaseName }
+ return columns.index { $0.0.lowercased() == lowercaseName }
Example 2 :
- .map { (mappedColumn, baseColumn) -> (Int, String) in
+ .map { (pair) -> (Int, String) in
+ let mappedColumn = pair.key
+ let baseColumn = pair.value
Example 3 :
- .map { (table, columns) in
"\(table)(\(columns.sorted().joined(separator: ", ")))" }
+ .map { "\($0.key)(\($0.value.sorted().joined(separator: ",
")))" }
Example 4 :
- dictionary.first { (column, value) in column.lowercased() ==
orderedColumn.lowercased() }
+ dictionary.first { $0.key.lowercased() ==
orderedColumn.lowercased() }
Gwendal Roué
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