How to write enum in smartPy?

Question

How do we translate the below enum in smartPy.

enum ServiceType {
        REQUEST_COIN_TRANSFER,
        REQUEST_COIN_REGISTER,
        REPONSE_HANDLE_SERVICE,
        BLACKLIST_MESSAGE,
        CHANGE_TOKEN_LIMIT,
        UNKNOWN_TYPE
    }

Answer 1

SmartPy offers the variant system (see doc for new and legacy syntax). It's more powerful than enum as they associate a value with a type so you can create enum with them and even more. Basically an enum is a variant with a sp.unit value.

I suggest you to take time to think how you can use the full power of it (not using a sp.unit value for each field.

New syntax

# Naming enum type
my_enum_type: type = sp.variant(REQUEST_COIN_TRANSFER=sp.unit, REQUEST_COIN_REGISTER=sp.unit...)

# Creating a value
my_value = sp.variant.REQUEST_COIN_TRANSFER(sp.unit)

# If the value is used somewhere the type isn't already enforced:
sp.cast(my_value, my_enum_type)

Legacy syntax

# Naming enum type
my_enum_type = sp.TVariant(REQUEST_COIN_TRANSFER=sp.TUnit, REQUEST_COIN_REGISTER=sp.TUnit...)

# Creating a value
my_value = sp.variant("REQUEST_COIN_TRANSFER", sp.unit)

# If the value is used somewhere the type isn't already enforced:
my_value = sp.set_type_expr(my_value, my_enum_type)

More examples can be found here: https://smartpy.io/ide?template=test_variant.py