Some adjectives, though being definite, are not constructed with ”den” and the noun in the definite. One of these is ”nästa”. You say
- Vad är nästa steg? (What is the next step.)
A similar one is ”samma” (same) and usually also ”följande” (following) and ”föregående” (preceding):
- Jag ska göra samma sak i dag. (I am going to do the same thing today.)
- Följande vecka ska vi titta på pronomen. (The following week we are going to look at pronouns.)
- Han gjorde samma sak som föregående vecka. (He did the same thing as the preceding week.)
In your examples with nästa, samma, följande, and föregående, the noun does not take the definite, e.g. "nästa fråga", not "nästa frågan." But with hela, it does - "hela dagen" "hela tiden" etc. not "hela dag" or "hela tid". So while they're the same with excluding den/det, the noun form is different.
So 2 questions then - 1) is hela the only one of these exceptions that still requires the definite form of the noun? 2) Is there a complete list anywhere of adjectives that don't require the definite form?
I think that samma, nästa, förande, föregående are special type of adjectives that have no other form than the afore mentioned, while hela has two more forms hel (for -en words) and helt (for -ett words). That is the reason why in the last example "hela dagen" one writes a definite form of the noun "dag", would you agree?
They’re almost always in separate syllables, i.e. the word consists of the following affixes: före-gå-ende, so it’s not a diphthong. In restaurang however, it’s a diphthong because it’s a loanword. Swedes don’t like diphthongs so it’s often just resturang in spoken language.