> On Apr 25, 2016, at 9:57 AM, Douglas Gregor <dgre...@apple.com> wrote:
>> On Apr 22, 2016, at 6:08 PM, John McCall <rjmcc...@apple.com
>> <mailto:rjmcc...@apple.com>> wrote:
>>
>>> On Apr 22, 2016, at 3:33 PM, Douglas Gregor via swift-dev
>>> <swift-dev@swift.org <mailto:swift-dev@swift.org>> wrote:
>>> Hi all,
>>>
>>> A common complaint with protocol conformance checking is that it’s easy to
>>> make a little mistake when trying to implement a protocol requirement that
>>> has a default implementation. Here is a silly example:
>>> [snip]
>>>
>>> Naturally, this handles typos as well, e.g.,
>>>
>>> t2.swift:12:8: warning: instance method 'foob(value:)' nearly matches
>>> optional requirement 'foo(value:)' of protocol 'P'
>>> func foob(value: Float) { }
>>> ^
>>> t2.swift:12:8: note: rename to 'foo(value:)' to satisfy this requirement
>>> func foob(value: Float) { }
>>> ^~~~
>>> foo
>>>
>>> Running this on the standard library produces a number of results:
>>>
>>> /Users/dgregor/Projects/swift/swift/stdlib/public/core/Arrays.swift.gyb:726:24:
>>> warning: instance method 'removeLast()' nearly matches optional
>>> requirement 'removeFirst()' of protocol 'RangeReplaceableCollection'
>>> public mutating func removeLast() -> Element {
>>> ^
>>> /Users/dgregor/Projects/swift/swift/stdlib/public/core/Arrays.swift.gyb:726:24:
>>> note: rename to 'removeFirst()' to satisfy this requirement
>>> public mutating func removeLast() -> Element {
>>> ^~~~~~~~~~
>>> removeFirst
>>> /Users/dgregor/Projects/swift/swift/stdlib/public/core/Arrays.swift.gyb:726:24:
>>> note: move 'removeLast()' to another extension to silence this warning
>>> public mutating func removeLast() -> Element {
>>> ^
>>> /Users/dgregor/Projects/swift/swift/stdlib/public/core/RangeReplaceableCollection.swift:158:17:
>>> note: requirement 'removeFirst()' declared here
>>> mutating func removeFirst() -> Iterator.Element
>>> ^
>>
>> Would a word-by-word edit-distance heuristic work better? That is,
>> removeFirst is not a plausible typo for removeLast because First is not a
>> plausible typo for Last.
>
> A word-by-word edit distance seems to imply that if *any* word is too far
> off, reject. I’m a bit concerned that it would create false negatives.
Any shift in the heuristic will eliminate false positives at the risk of
creating false negatives.
A word-by-word heuristic allows you to catch a large number of typos in a long
method name without matching completely different words just because the method
name is long. That seems like the right trade-off to me.
> One possibility in this space would be to remove common words from
> consideration. That way, only the mismatching words will be used to do the
> edit-distance computation, so the one-mistake-per-N-characters-typed
> heuristic wouldn’t consider the completely-matching parts.
I think you have fallen a bit too in love with dictionaries.
> In defense of the warning in this case: RangeReplaceableCollection has a
> “removeFirst” but not a “removeLast”; the conforming type here is
> implementing “removeLast” but not “removeFirst”. It is *so easy* to imagine
> this as programmer error that the warning feels justified.
This does not feel like it leads to a reasonable general principle. At best it
calls for some way to opt in to a warning about implementing only "related"
methods, analogous the related-type warnings in ObjC ARC bridging.
John.
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