Lesson 35 · Matching the original case

Matching the original case

A suggestion should look like what the user typed - correcting "Teh" to lower-case "the" feels broken. Today you restore the original word's capitalization pattern onto each suggestion.

The goal

Reshape a lower-case suggestion to match the capitalization pattern of the word it corrects.

Start here - the target

TO DO

Scenario: Restoring capitalization onto suggestions

Giventhe lower-case correction "the"

Whenits case is matched to the original typed word

ThenMatchCase("the", "Teh") is "The" and MatchCase("the", "TEH") is "THE"

AndMatchCase("the", "teh") is "the" (all lower-case stays lower-case)

Background

Corrections are generated and stored in lower case, but a user who typed Teh at the start of a sentence expects The, not the. So the last step before showing a suggestion is to restore the case of the original word onto it: an all-caps typo gets an all-caps fix, a leading-capital typo gets a leading-capital fix, and an ordinary lower-case word is left alone.

The three patterns - all upper, title case, all lower - cover the vast majority of real writing, and matching them makes the tool feel like it understands the text rather than mechanically lower-casing everything. The Checker applies MatchCase to each suggestion as it fills an Issue, using the token’s original text as the template, so Suggestions come out looking like drop-in replacements for what was typed.

Make it work

func MatchCase(suggestion, original string) string {
  // if original is all upper-case  -> upper-case the suggestion
  // if original is title-case (first letter upper, rest not)
  //                                 -> title-case the suggestion
  // otherwise                       -> leave it lower-case
}

CheckpointDONE

Suggestions now mirror the capitalization of the word they replace. Commit and stop here.