SmartPy, File "smartML/tools/compiler.ml", line 2210, characters 18-24: Assertion failed

Question

I am creating a big_maps with a value type of struct Assets and AssetsDetails. While i try to put the value in map getting an error of: [error] File "smartML/tools/compiler.ml", line 2210, characters 18-24: Assertion failed. The error is from this part of code: assets[i]=sp.record( coin_name=coin_names[i], value=values[i], )

Here is the code:

import smartpy as sp

Asset = sp.TRecord(
    coin_name=sp.TString,
    value=sp.TNat
    )

class Preiphery(sp.Contract):
    @sp.entry_point
    def send_service_message(self, _from, to, coin_names, values, fees):
        sp.set_type(_from, sp.TAddress)
        sp.set_type(to, sp.TString)
        sp.set_type(coin_names, sp.TMap(sp.TNat, sp.TString))
        sp.set_type(values, sp.TMap(sp.TNat, sp.TNat))
        sp.set_type(fees, sp.TMap(sp.TNat, sp.TNat))

        assets = sp.big_map(tkey=sp.TNat, tvalue=Asset)

        sp.for i in sp.range(sp.nat(0), sp.len(coin_names)):
            assets[i]=sp.record(
                coin_name=coin_names[i],
                value=values[i]
            )

@sp.add_test(name="Counter")
def test():
    scenario = sp.test_scenario()
    counter = Preiphery()
    scenario += counter

Answer 1

In the legacy syntax sp.big_map(...) does not create a big_map. It only returns an expression that, when evaluated, creates a big_map.

If you want to modify a variable you have to use a sp.local. As big_map are only updated through methods you can even simplify and use sp.compute.

 assets = sp.compute(sp.big_map(tkey=sp.TNat, tvalue=Asset))

Now let me add that it's strange having to do what you are doing. Why not giving a more proximate type in the entrypoint?

class Preiphery(sp.Contract):
    @sp.entry_point
    def send_service_message(self, _from, to, coins):
        sp.set_type(_from, sp.TAddress)
        sp.set_type(to, sp.TString)
        sp.set_type(coins, sp.TList(Asset))

        assets = sp.compute(sp.big_map(tkey=sp.TNat, tvalue=Asset))
        i = sp.local("i", 0)

        sp.for coin in coins:
            assets[i.value]=coin
            i.value += 1

Would do the same thing.