If I visit a friend, and he/she asks me a question like this:
My friend: What would you like to drink?
Me: I’ll have an orange juice, please.
I understand we use “I’ll” (“I will”) when we decide to do something at the time of speaking, such as in the former case.
However, what if I want to drink an orange juice at a coffee shop (because it’s very delicious)? I already planned to buy it before I went to the shop. How can I answer this question at the coffee shop?
Waitress: What would you like to drink?
Can I say “I’m going to have an orange juice.”?