I've read a bit about the partitive genitive in Russian, used in expressions such as "кусок сахару", "чашка чаю".
However, the sources I use usually label this declension as facultative, mainly literary.
1. So, are "кусок сахару" and "чашка чаю" just alternatives to "кусок сахара" and "чашка чая" respectively?
2. Second question: It's told that the partitive genitive, when used to talk about an indefinite amount of a commodity, is analogous to the French usage of de / du / de la.
In French it's common to say "Je veux du thé" ("I want [an indefinite amount of] tea").
Has partitive genitive in Russian the same function here? Like, "Я хочу чаю", "Я хочу сыру", in order to express desire for an indefinite amount of a feeding commodity?
3. As far as I know, the verb "хотеть" is followed either by accusative (when referring to concrete nouns in general) and genitive (regarding abstract nouns such as in the expression "Я хочу мира", or negation).
When referring to a commodity such as чай, сыр, сахар, is it better to use accusative ("Я хочу чай") or genitive? If genitive, may I use "Я хочу чая" and "Я хочу чаю" interchangeably, or just чаю?