文字列の各単語の最初の文字を大文字に変換し、残りをそのままにする CapitalizeWords <T> を実装します。
例えば
type capitalized = CapitalizeWords<'hello world, my friends'> // expected to be 'Hello World, My Friends'
import type { Equal, Expect } from '@type-challenges/utils'
type cases = [
Expect<Equal<CapitalizeWords<'foobar'>, 'Foobar'>>,
Expect<Equal<CapitalizeWords<'FOOBAR'>, 'FOOBAR'>>,
Expect<Equal<CapitalizeWords<'foo bar'>, 'Foo Bar'>>,
Expect<Equal<CapitalizeWords<'foo bar hello world'>, 'Foo Bar Hello World'>>,
Expect<Equal<CapitalizeWords<'foo bar.hello,world'>, 'Foo Bar.Hello,World'>>,
Expect<Equal<CapitalizeWords<'aa!bb@cc#dd$ee%ff^gg&hh*ii(jj)kk_ll+mm{nn}oo|pp🤣qq'>, 'Aa!Bb@Cc#Dd$Ee%Ff^Gg&Hh*Ii(Jj)Kk_Ll+Mm{Nn}Oo|Pp🤣Qq'>>,
Expect<Equal<CapitalizeWords<''>, ''>>,
]