`TokenSymbol::try_from(Felt)` does not error on underflow

[Mirko-von-Leipzig]

TokenSymbol::try_from(Felt::ZERO) should fail, but it does not as it only checks against the maximum value.

I guess it needs a

const MIN_ENCODED_VALUE: u64 = Self::from_static("A").0.as_int();

and an additional check.

As a separate issue, I'm also surprised that TokenSymbol::to_string is fallible -- surely it should always succeed?

[PhilippGackstatter]

Thanks for the report! I think this is why it's generally best to have a single constructor for a type (that does validation) and that is the only place allowed to instantiate the struct directly. An exception are _unchecked constructors.

I think defining it as TokenSymbol(String) would be better for the overall API, only doing encoding when converting to Felt and not needing decode logic when calling to_string. Decoding would only be needed in TokenSymbol::try_from(felt). Then we can also replace to_string with as_str(&self) -> &str.

[Himess]

Can i take it ?