ToBigInt and ToBigUint should not return an error

[rust-highfive]

Issue by lifthrasiir
Wednesday Apr 16, 2014 at 10:23 GMT

For earlier discussion, see rust-lang/rust#13555

This issue was labelled with: in the Rust repository

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It is a side effect of #9250, which added those traits as a special case of the FromPrimitive trait. This is rather strange, since the current ToBigInt implementors do not fail at all ( ToBigUint does fail, but only because they are implemented for signed integers as well).

Given that BigInt and BigUint already implements FromStr (that would correspond to impl<'a> ToBigInt for &'a str and so on), it would be better to make them implemented only for types that would definitely convertible to the big integers without an error. More precisely:

• Make ToBigInt::to_bigint and ToBigUint::to_biguint return BigInt and BigUint respectively.
• Remove implementations of ToBigUint for signed integers and BigInt.
• Add a new into_biguint (since it's more efficient, and does not confuse users of ToBigUint) to BigInt, which returns Option<BigUint>. We may also have into_bigint to BigUint, at expense of symmetry (it becomes asymmetric since it should not return Option<BigInt>).

[nrc]

Wrong repo